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113-426: In general, when data corruption occurs, a file containing that data will produce unexpected results when accessed by the system or the related application. Results could range from a minor loss of data to a system crash. For example, if a document file is corrupted, when a person tries to open that file with a document editor they may get an error message , thus the file might not be opened or might open with some of

226-707: A file of punched cards ." In February 1950, in a Radio Corporation of America (RCA) advertisement in Popular Science magazine describing a new "memory" vacuum tube it had developed, RCA stated: "the results of countless computations can be kept 'on file' and taken out again. Such a 'file' now exists in a 'memory' tube developed at RCA Laboratories. Electronically it retains figures fed into calculating machines, holds them in storage while it memorizes new ones – speeds intelligent solutions through mazes of mathematics." In 1952, "file" denoted, among other things, information stored on punched cards . In early use,

339-471: A computer storage device , primarily identified by its filename . Just as words can be written on paper, so too can data be written to a computer file. Files can be shared with and transferred between computers and mobile devices via removable media , networks , or the Internet . Different types of computer files are designed for different purposes. A file may be designed to store a written message,

452-462: A hard disk . Hard disks have been the ubiquitous form of non-volatile storage since the early 1960s. Where files contain only temporary information, they may be stored in RAM . Computer files can be also stored on other media in some cases, such as magnetic tapes , compact discs , Digital Versatile Discs , Zip drives , USB flash drives , etc. The use of solid state drives is also beginning to rival

565-428: A link to the file. There can be many links to a file, but when they are all removed, the kernel considers that file's memory space free to be reallocated. This free space is commonly considered a security risk (due to the existence of file recovery software ). Any secure-deletion program uses kernel-space (system) functions to wipe the file's data. File moves within a file system complete almost immediately because

678-454: A FAT extension allowing long file names). File manager programs are utility programs that allow users to manipulate files directly. They allow you to move, create, delete and rename files and folders, although they do not actually allow you to read the contents of a file or store information in it. Every computer system provides at least one file-manager program for its native file system. For example, File Explorer (formerly Windows Explorer)

791-913: A RAID-Z block, ZFS compares it against its checksum, and if the data disks did not return the right answer, ZFS reads the parity and then figures out which disk returned bad data. Then, it repairs the damaged data and returns good data to the requestor. RAID-Z and mirroring do not require any special hardware: they do not need NVRAM for reliability, and they do not need write buffering for good performance or data protection. With RAID-Z, ZFS provides fast, reliable storage using cheap, commodity disks. There are five different RAID-Z modes: striping (similar to RAID 0, offers no redundancy), RAID-Z1 (similar to RAID 5, allows one disk to fail), RAID-Z2 (similar to RAID 6, allows two disks to fail), RAID-Z3 (a RAID 7 configuration, allows three disks to fail), and mirroring (similar to RAID 1, allows all but one disk to fail). The need for RAID-Z3 arose in

904-418: A block is accessed, regardless of whether it is data or meta-data, its checksum is calculated and compared with the stored checksum value of what it "should" be. If the checksums match, the data are passed up the programming stack to the process that asked for it; if the values do not match, then ZFS can heal the data if the storage pool provides data redundancy (such as with internal mirroring ), assuming that

1017-460: A closed source license when Oracle Corporation acquired Sun in 2009–2010. During 2005 to 2010, the open source version of ZFS was ported to Linux , Mac OS X (continued as MacZFS ) and FreeBSD . In 2010, the illumos project forked a recent version of OpenSolaris, including ZFS, to continue its development as an open source project. In 2013, OpenZFS was founded to coordinate the development of open source ZFS. OpenZFS maintains and manages

1130-412: A corruption is detected and the file system uses integrated RAID mechanisms that provide data redundancy , such file systems can also reconstruct corrupted data in a transparent way. This approach allows improved data integrity protection covering the entire data paths, which is usually known as end-to-end data protection , compared with other data integrity approaches that do not span different layers in

1243-427: A device, no space will have been freed up on the source device or partition. The user would need to merge the remaining files from the source, including the incompletely written (truncated) last file. With the individual deletion method, the file moving software also does not need to cumulatively keep track of all files finished transferring for the case that a user manually aborts the file transfer. A file manager using

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1356-524: A directory and a file. In environments in which a file is named, a file's name and the path to the file's directory must uniquely identify it among all other files in the computer system—no two files can have the same name and path. Where a file is anonymous, named references to it will exist within a namespace. In most cases, any name within the namespace will refer to exactly zero or one file. However, any file may be represented within any namespace by zero, one or more names. Any string of characters may be

1469-425: A document, a spreadsheet , an image , a video , a program , or any wide variety of other kinds of data. Certain files can store multiple data types at once. By using computer programs, a person can open, read, change, save, and close a computer file. Computer files may be reopened, modified, and copied an arbitrary number of times. Files are typically organized in a file system , which tracks file locations on

1582-847: A dot (period) at the end of a file name, followed by a few letters to identify the type of file. An extension of .txt identifies a text file; a .doc extension identifies any type of document or documentation, commonly in the Microsoft Word file format ; and so on . Even when extensions are used in a computer system, the degree to which the computer system recognizes and heeds them can vary; in some systems, they are required, while in other systems, they are completely ignored if they are presented. Many modern computer systems provide methods for protecting files against accidental and deliberate damage. Computers that allow for multiple users implement file permissions to control who may or may not modify, delete, or create files and folders. For example,

1695-514: A given user may be granted only permission to read a file or folder, but not to modify or delete it; or a user may be given permission to read and modify files or folders, but not to execute them. Permissions may also be used to allow only certain users to see the contents of a file or folder. Permissions protect against unauthorized tampering or destruction of information in files, and keep private information confidential from unauthorized users. Another protection mechanism implemented in many computers

1808-446: A later point through overwriting. There are many ways by which a file can become corrupted. Most commonly, the issue happens in the process of writing the file to a disk . For example, if an image-editing program unexpectedly crashes while saving an image, that file may be corrupted because the program could not save its entirety. The program itself might warn the user that there was an error, allowing for another attempt at saving

1921-461: A limited number of devices. It also means that when data is read (and reads are much more frequent than writes in most uses), different parts of the data can be read from as many disks as possible at the same time, giving much higher read performance. Therefore, as a general rule, pools and vdevs should be managed and new storage added, so that the situation does not arise that some vdevs in a pool are almost full and others almost empty, as this will make

2034-420: A low level, on a file. Only the kernel deals with files, and it handles all user-space interaction with files in a manner that is transparent to the user-space programs. The operating system provides a level of abstraction , which means that interaction with a file from user-space is simply through its filename (instead of its inode ). For example, rm filename will not delete the file itself, but only

2147-503: A month, and cheaper commodity disks once a week. ZFS is a 128-bit file system, so it can address 1.84 × 10 times more data than 64-bit systems such as Btrfs . The maximum limits of ZFS are designed to be so large that they should never be encountered in practice. For instance, fully populating a single zpool with 2 bits of data would require 3×10  TB hard disk drives. Some theoretical limits in ZFS are: With Oracle Solaris,

2260-406: A name of its own, but also a path, which identifies the folder or folders in which a file or folder resides. In the path, some sort of special character—such as a slash—is used to separate the file and folder names. For example, in the illustration shown in this article, the path /Payroll/Salaries/Managers uniquely identifies a file called Managers in a folder called Salaries , which in turn

2373-418: A number of bytes , that indicates how much storage is occupied by the file. In most modern operating systems the size can be any non-negative whole number of bytes up to a system limit. Many older operating systems kept track only of the number of blocks or tracks occupied by a file on a physical storage device. In such systems, software employed other methods to track the exact byte count (e.g., CP/M used

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2486-443: A payroll file might contain information concerning all the employees in a company and their payroll details; each record in the payroll file concerns just one employee, and all the records have the common trait of being related to payroll—this is very similar to placing all payroll information into a specific filing cabinet in an office that does not have a computer. A text file may contain lines of text, corresponding to printed lines on

2599-429: A piece of paper. Alternatively, a file may contain an arbitrary binary image (a blob ) or it may contain an executable . The way information is grouped into a file is entirely up to how it is designed. This has led to a plethora of more or less standardized file structures for all imaginable purposes, from the simplest to the most complex. Most computer files are used by computer programs which create, modify or delete

2712-408: A rate of several in thousands of cores. One problem is that hard disk drive capacities have increased substantially, but their error rates remain unchanged. The data corruption rate has always been roughly constant in time, meaning that modern disks are not much safer than old disks. In old disks the probability of data corruption was very small because they stored tiny amounts of data. In modern disks

2825-529: A single system without the low level view ZFS relies upon, there is a much greater chance that the system will perform less optimally and that ZFS will be less likely to prevent failures, recover from failures more slowly, or lose data due to a write failure. For example, if a hardware RAID card is used, ZFS may not be able to determine the condition of disks, determine if the RAID array is degraded or rebuilding, detect all data corruption, place data optimally across

2938-433: A special control character, Ctrl-Z , to signal the end of text files). The general definition of a file does not require that its size have any real meaning, however, unless the data within the file happens to correspond to data within a pool of persistent storage. A special case is a zero byte file ; these files can be newly created files that have not yet had any data written to them, or may serve as some kind of flag in

3051-458: A total of four caches. This becomes crucial if a large number of synchronous writes take place (such as with ESXi , NFS and some databases ), where the client requires confirmation of successful writing before continuing its activity; the SLOG allows ZFS to confirm writing is successful much more quickly than if it had to write to the main store every time, without the risk involved in misleading

3164-438: A tree-like structure in which one "master folder" (or "root folder" — the name varies from one operating system to another) can contain any number of levels of other folders and files. Folders can be named just as files can (except for the root folder, which often does not have a name). The use of folders makes it easier to organize files in a logical way. When a computer allows the use of folders, each file and folder has not only

3277-477: A variety of causes. Interruption of data transmission causes information loss . Environmental conditions can interfere with data transmission, especially when dealing with wireless transmission methods. Heavy clouds can block satellite transmissions. Wireless networks are susceptible to interference from devices such as microwave ovens. Hardware and software failure are the two main causes for data loss . Background radiation , head crashes , and aging or wear of

3390-400: A virus or trojan with this payload method manages to alter files critical to the running of the computer's operating system software or physical hardware, the entire system may be rendered unusable. Some programs can give a suggestion to repair the file automatically (after the error), and some programs cannot repair it. It depends on the level of corruption, and the built-in functionality of

3503-419: A well-formed name for a file or a link depending upon the context of application. Whether or not a name is well-formed depends on the type of computer system being used. Early computers permitted only a few letters or digits in the name of a file, but modern computers allow long names (some up to 255 characters) containing almost any combination of Unicode letters or Unicode digits, making it easier to understand

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3616-436: Is a read-only flag. When this flag is turned on for a file (which can be accomplished by a computer program or by a human user), the file can be examined, but it cannot be modified. This flag is useful for critical information that must not be modified or erased, such as special files that are used only by internal parts of the computer system. Some systems also include a hidden flag to make certain files invisible; this flag

3729-399: Is a data/parity distribution scheme like RAID-5 , but uses dynamic stripe width: every block is its own RAID stripe, regardless of blocksize, resulting in every RAID-Z write being a full-stripe write. This, when combined with the copy-on-write transactional semantics of ZFS, eliminates the write hole error . RAID-Z is also faster than traditional RAID 5 because it does not need to perform

3842-450: Is also faster than UFS and can be seen as its replacement. Within ZFS, data integrity is achieved by using a Fletcher-based checksum or a SHA-256 hash throughout the file system tree. Each block of data is checksummed and the checksum value is then saved in the pointer to that block—rather than at the actual block itself. Next, the block pointer is checksummed, with the value being saved at its pointer. This checksumming continues all

3955-479: Is an area of memory which is manipulated to establish a filename etc. and then passed to the operating system as a parameter; it was used by older IBM operating systems and early PC operating systems including CP/M and early versions of MS-DOS . A file handle is generally either an opaque data type or an integer; it was introduced in around 1961 by the ALGOL-based Burroughs MCP running on

4068-700: Is automatically cached in a hierarchy to optimize performance versus cost; these are often called "hybrid storage pools". Frequently accessed data will be stored in RAM, and less frequently accessed data can be stored on slower media, such as solid-state drives (SSDs). Data that is not often accessed is not cached and left on the slow hard drives. If old data is suddenly read a lot, ZFS will automatically move it to SSDs or to RAM. ZFS caching mechanisms include one each for reads and writes, and in each case, two levels of caching can exist, one in computer memory (RAM) and one on fast storage (usually solid-state drives (SSDs)), for

4181-492: Is available on Intel Itanium processors. Many errors are detected and corrected by the hard disk drives using the ECC codes which are stored on disk for each sector. If the disk drive detects multiple read errors on a sector it may make a copy of the failing sector on another part of the disk, by remapping the failed sector of the disk to a spare sector without the involvement of the operating system (though this may be delayed until

4294-425: Is available to all of the file system instances in the zpool. A quota can be set to limit the amount of space a file system instance can occupy, and a reservation can be set to guarantee that space will be available to a file system instance. ZFS uses different layers of disk cache to speed up read and write operations. Ideally, all data should be stored in RAM, but that is usually too expensive. Therefore, data

4407-621: Is commonly used in Microsoft Windows operating systems, and Nautilus is common under several distributions of Linux. ZFS ZFS (previously Zettabyte File System ) is a file system with volume management capabilities. It began as part of the Sun Microsystems Solaris operating system in 2001. Large parts of Solaris, including ZFS, were published under an open source license as OpenSolaris for around 5 years from 2005 before being placed under

4520-420: Is contained in a folder called Payroll . The folder and file names are separated by slashes in this example; the topmost or root folder has no name, and so the path begins with a slash (if the root folder had a name, it would precede this first slash). Many computer systems use extensions in file names to help identify what they contain, also known as the file type. On Windows computers, extensions consist of

4633-464: Is corrupted. There are services that provide on demand file corruption, which essentially fill a given file with random data so that it cannot be opened or read, yet still seems legitimate. One of the most effective countermeasures for unintentional file corruption is backing up important files. In the event of an important file becoming corrupted, the user can simply replace it with the backed up version. When computer files contain information that

Data corruption - Misplaced Pages Continue

4746-613: Is extremely important, a back-up process is used to protect against disasters that might destroy the files. Backing up files simply means making copies of the files in a separate location so that they can be restored if something happens to the computer, or if they are deleted accidentally. There are many ways to back up files. Most computer systems provide utility programs to assist in the back-up process, which can become very time-consuming if there are many files to safeguard. Files are often copied to removable media such as writable CDs or cartridge tapes. Copying files to another hard disk in

4859-418: Is for the wrapping key to be inherited by any child data sets. The data encryption keys are randomly generated at dataset creation time. Only descendant datasets (snapshots and clones) share data encryption keys. A command to switch to a new data encryption key for the clone or at any time is provided—this does not re-encrypt already existing data, instead utilising an encrypted master-key mechanism. As of 2019

4972-403: Is particularly important in commercial applications (e.g. banking ), where an undetected error could either corrupt a database index or change data to drastically affect an account balance, and in the use of encrypted or compressed data, where a small error can make an extensive dataset unusable. Computer file In computing , a computer file is a resource for recording data on

5085-565: Is strongly recommended that these methods not be used as they typically reduce the system's performance and reliability. If disks must be attached through a RAID or other controller, it is recommended to minimize the amount of processing done in the controller by using a plain HBA (host adapter) , a simple fanout card, or configure the card in JBOD mode (i.e. turn off RAID and caching functions), to allow devices to be attached with minimal changes in

5198-415: Is that it is designed with a focus on data integrity by protecting the user's data on disk against silent data corruption caused by data degradation , power surges ( voltage spikes ), bugs in disk firmware , phantom writes (the previous write did not make it to disk), misdirected reads/writes (the disk accesses the wrong block), DMA parity errors between the array and server memory or from the driver (since

5311-435: Is used by the computer system to hide essential system files that users should not alter. Any file that has any useful purpose must have some physical manifestation. That is, a file (an abstract concept) in a real computer system must have a real physical analogue if it is to exist at all. In physical terms, most computer files are stored on some type of data storage device. For example, most operating systems store files on

5424-493: Is used in its corrupted state. When data corruption behaves as a Poisson process , where each bit of data has an independently low probability of being changed, data corruption can generally be detected by the use of checksums , and can often be corrected by the use of error correcting codes (ECC). If an uncorrectable data corruption is detected, procedures such as automatic retransmission or restoration from backups can be applied. Certain levels of RAID disk arrays have

5537-627: The mv command for instance, the former method is used when selecting files individually, possibly with the use of wildcards (example: mv -n sourcePath/* targetPath , while the latter method is used when selecting entire directories (example: mv -n sourcePath targetPath ). Microsoft Windows Explorer uses the former method for mass storage file moves, but the latter method using Media Transfer Protocol , as described in Media Transfer Protocol § File move behavior . The former method (individual deletion from source) has

5650-468: The Burroughs B5000 but is now ubiquitous. When a file is said to be corrupted, it is because its contents have been saved to the computer in such a way that they cannot be properly read, either by a human or by software. Depending on the extent of the damage, the original file can sometimes be recovered , or at least partially understood. A file may be created corrupt, or it may be corrupted at

5763-798: The FreeBSD documentation as one of its "most powerful features" with functionality that "even other file systems with snapshot functionality lack". Very large numbers of snapshots can be taken without degrading performance, allowing snapshots to be used prior to risky system operations and software changes, or an entire production ("live") file system to be fully snapshotted several times an hour in order to mitigate data loss due to user error or malicious activity. Snapshots can be rolled back "live" or previous file system states can be viewed, even on very large file systems, leading to savings in comparison to formal backup and restore processes. Snapshots can also be cloned to form new independent file systems. ZFS also has

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5876-619: The NTFS file system that is the normal file system for recent versions of Windows. Each system has its own advantages and disadvantages. Standard FAT allows only eight-character file names (plus a three-character extension) with no spaces, for example, whereas NTFS allows much longer names that can contain spaces. You can call a file " Payroll records " in NTFS, but in FAT you would be restricted to something like payroll.dat (unless you were using VFAT ,

5989-445: The operating system (often involving a volume manager , RAID controller , array manager, or suitable device driver ); and the management of data and files that are stored on these logical block devices (a file system or other data storage). ZFS is unusual because, unlike most other storage systems, it unifies both of these roles and acts as both the volume manager and the file system . Therefore, it has complete knowledge of both

6102-737: The ZFS-to-disk I/O pathway. A RAID card in JBOD mode may still interfere if it has a cache or, depending upon its design, may detach drives that do not respond in time (as has been seen with many energy-efficient consumer-grade hard drives), and as such, may require Time-Limited Error Recovery (TLER)/CCTL/ERC-enabled drives to prevent drive dropouts, so not all cards are suitable even with RAID functions disabled. Instead of hardware RAID, ZFS employs "soft" RAID, offering RAID-Z ( parity based like RAID 5 and similar) and disk mirroring (similar to RAID 1 ). The schemes are highly flexible. RAID-Z

6215-476: The ability to store and evaluate parity bits for data across a set of hard disks and can reconstruct corrupted data upon the failure of a single or multiple disks, depending on the level of RAID implemented. Some CPU architectures employ various transparent checks to detect and mitigate data corruption in CPU caches , CPU buffers and instruction pipelines ; an example is Intel Instruction Replay technology, which

6328-472: The ability to take a pool level snapshot (known as a "checkpoint"), which allows rollback of operations that may affect the entire pool's structure or that add or remove entire datasets. In 1987, AT&T Corporation and Sun announced that they were collaborating on a project to merge the most popular Unix variants on the market at that time: Berkeley Software Distribution , UNIX System V , and Xenix . This became Unix System V Release 4 (SVR4). The project

6441-444: The application to handle the error. There are various causes of the corruption. There are two types of data corruption associated with computer systems: undetected and detected. Undetected data corruption, also known as silent data corruption , results in the most dangerous errors as there is no indication that the data is incorrect. Detected data corruption may be permanent with the loss of data, or may be temporary when some part of

6554-410: The archive file are to lower the number of files for easier transfer, to reduce storage usage, or just to organize outdated files. The archive file must often be unpacked before next using. The most basic operations that programs can perform on a file are: Files on a computer can be created, moved, modified, grown, shrunk ( truncated ), and deleted. In most cases, computer programs that are executed on

6667-407: The benefit that space is released from the source device or partition imminently after the transfer has begun, meaning after the first file is finished. With the latter method, space is only freed after the transfer of the entire selection has finished. If an incomplete file transfer with the latter method is aborted unexpectedly, perhaps due to an unexpected power-off, system halt or disconnection of

6780-535: The capability to check in-memory data exists and can be enabled using "debug flags". For ZFS to be able to guarantee data integrity, it needs multiple copies of the data or parity information, usually spread across multiple disks. This is typically achieved by using either a RAID controller or so-called "soft" RAID (built into a file system ). While ZFS can work with hardware RAID devices, it will usually work more efficiently and with greater data protection if it has raw access to all storage devices. ZFS relies on

6893-412: The chance of data loss by simply increasing redundancy. ZFS has no tool equivalent to fsck (the standard Unix and Linux data checking and repair tool for file systems). Instead, ZFS has a built-in scrub function which regularly examines all data and repairs silent corruption and other problems. Some differences are: The official recommendation from Sun/Oracle is to scrub enterprise-level disks once

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7006-536: The checksum validates data inside the array), driver errors (data winds up in the wrong buffer inside the kernel), accidental overwrites (such as swapping to a live file system), etc.. A 1999 study showed that neither any of the then-major and widespread filesystems (such as UFS , Ext , XFS , JFS , or NTFS ), nor hardware RAID (which has some issues with data integrity ) provided sufficient protection against data corruption problems. Initial research indicates that ZFS protects data better than earlier efforts. It

7119-405: The client as to the state of data storage. If there is no SLOG device then part of the main data pool will be used for the same purpose, although this is slower. If the log device itself is lost, it is possible to lose the latest writes, therefore the log device should be mirrored. In earlier versions of ZFS, loss of the log device could result in loss of the entire zpool, although this is no longer

7232-559: The computer handle these operations, but the user of a computer can also manipulate files if necessary. For instance, Microsoft Word files are normally created and modified by the Microsoft Word program in response to user commands, but the user can also move, rename , or delete these files directly by using a file manager program such as Windows Explorer (on Windows computers) or by command lines (CLI). In Unix-like systems, user space programs do not operate directly, at

7345-400: The copy of data is undamaged and with matching checksums. It is optionally possible to provide additional in-pool redundancy by specifying copies=2 (or copies=3 ), which means that data will be stored twice (or three times) on the disk, effectively halving (or, for copies=3 , reducing to one-third) the storage capacity of the disk. Additionally, some kinds of data used by ZFS to manage

7458-534: The core ZFS code, while organizations using ZFS maintain the specific code and validation processes required for ZFS to integrate within their systems. OpenZFS is widely used in Unix-like systems. The management of stored data generally involves two aspects: the physical volume management of one or more block storage devices (such as hard drives and SD cards ), including their organization into logical block devices as VDEVs (ZFS Virtual Device) as seen by

7571-410: The data content does not need to be rewritten. Only the paths need to be changed. There are two distinct implementations of file moves. When moving files between devices or partitions, some file managing software deletes each selected file from the source directory individually after being transferred, while other software deletes all files at once only after every file has been transferred. With

7684-432: The data corrupted (or in some cases, completely corrupted, leaving the document unintelligible). The adjacent image is a corrupted image file in which most of the information has been lost. Some types of malware may intentionally corrupt files as part of their payloads , usually by overwriting them with inoperative or garbage code, while a non-malicious virus may also unintentionally corrupt files when it accesses them. If

7797-407: The data with another compatible controller, but this isn't always possible and a replacement may not be available. Alternate hardware RAID controllers may not understand the original manufacturer's custom data required to manage and restore an array. Unlike most other systems where RAID cards or similar hardware can offload resources and processing to enhance performance and reliability, with ZFS it

7910-706: The disk and enables user access. The word "file" derives from the Latin filum ("a thread, string"). "File" was used in the context of computer storage as early as January 1940. In Punched Card Methods in Scientific Computation , W. J. Eckert stated, "The first extensive use of the early Hollerith Tabulator in astronomy was made by Comrie . He used it for building a table from successive differences, and for adding large numbers of harmonic terms". "Tables of functions are constructed from their differences with great efficiency, either as printed tables or as

8023-525: The disk for an honest view to determine the moment data is confirmed as safely written and has numerous algorithms designed to optimize its use of caching , cache flushing , and disk handling. Disks connected to the system using a hardware, firmware, other "soft" RAID, or any other controller that modifies the ZFS-to-disk I/O path will affect ZFS performance and data integrity. If a third-party device performs caching or presents drives to ZFS as

8136-423: The disk, often done as a low priority background process. The "data scrubbing" operation activates a parity check. If a user simply runs a normal program that reads data from the disk, then the parity would not be checked unless parity-check-on-read was both supported and enabled on the disk subsystem. If appropriate mechanisms are employed to detect and remedy data corruption, data integrity can be maintained. This

8249-406: The disks, make selective repairs, control how repairs are balanced with ongoing use, or make repairs that ZFS could usually undertake. The hardware RAID card will interfere with ZFS' algorithms. RAID controllers also usually add controller-dependent data to the drives which prevents software RAID from accessing the user data. In the case of a hardware RAID controller failure, it may be possible to read

8362-440: The document file is arranged in a format that the word-processing program understands, the user is able to choose the name and location of the file and provide the bulk of the information (such as words and text) that will be stored in the file. Many applications pack all their data files into a single file called an archive file , using internal markers to discern the different types of information contained within. The benefits of

8475-438: The early 2000s as multi-terabyte capacity drives became more common. This increase in capacity—without a corresponding increase in throughput speeds—meant that rebuilding an array due to a failed drive could "easily take weeks or months" to complete. During this time, the older disks in the array will be stressed by the additional workload, which could result in data corruption or drive failure. By increasing parity, RAID-Z3 reduces

8588-467: The encryption capability in ZFS is embedded into the I/O pipeline. During writes, a block may be compressed, encrypted, checksummed and then deduplicated, in that order. The policy for encryption is set at the dataset level when datasets (file systems or ZVOLs) are created. The wrapping keys provided by the user/administrator can be changed at any time without taking the file system offline. The default behaviour

8701-412: The encryption feature is also fully integrated into OpenZFS 0.8.0 available for Debian and Ubuntu Linux distributions. There have been anecdotal end-user reports of failures when using ZFS native encryption. An exact cause has not been established. ZFS will automatically allocate data storage across all vdevs in a pool (and all devices in each vdev) in a way that generally maximises the performance of

8814-403: The existence of directory hierarchies, i.e., directories containing sub-directories. A name that refers to a file within a directory must be typically unique. In other words, there must be no identical names within a directory. However, in some operating systems, a name may include a specification of type that means a directory can contain an identical name for more than one type of object such as

8927-641: The fast database at Greenplum , which is a database software company specializing in large-scale data warehousing and analytics, faces silent corruption every 15 minutes. As another example, a real-life study performed by NetApp on more than 1.5 million HDDs over 41 months found more than 400,000 silent data corruptions, out of which more than 30,000 were not detected by the hardware RAID controller (only detected during scrubbing ). Another study, performed by CERN over six months and involving about 97  petabytes of data, found that about 128  megabytes of data became permanently corrupted silently somewhere in

9040-414: The file and the son is the current copy. The way a computer organizes, names, stores and manipulates files is globally referred to as its file system . Most computers have at least one file system. Some computers allow the use of several different file systems. For instance, on newer MS Windows computers, the older FAT-type file systems of MS-DOS and old versions of Windows are supported, in addition to

9153-414: The file system) file-specific data outside of the file format, but linked to the file, for example extended attributes or forks . On other file systems this can be done via sidecar files or software-specific databases. All those methods, however, are more susceptible to loss of metadata than container and archive file formats. At any instant in time, a file has a specific size, normally expressed as

9266-526: The file system, or are accidents (the results of aborted disk operations). For example, the file to which the link /bin/ls points in a typical Unix-like system probably has a defined size that seldom changes. Compare this with /dev/null which is also a file, but as a character special file , its size is not meaningful. Information in a computer file can consist of smaller packets of information (often called " records " or "lines") that are individually different but share some common traits. For example,

9379-423: The file. Some other examples of reasons for which files become corrupted include: Although file corruption usually happens accidentally, it may also be done on purpose as a mean of procrastination , as to fool someone else into thinking an assignment was ready at an earlier date, potentially gaining time to finish said assignment or making experiments, with the purpose of documenting the consequences when such file

9492-402: The files for their own use on an as-needed basis. The programmers who create the programs decide what files are needed, how they are to be used and (often) their names. In some cases, computer programs manipulate files that are made visible to the computer user. For example, in a word-processing program , the user manipulates document files that the user personally names. Although the content of

9605-447: The filesystem can continue in the case of the failure of an entire chassis. Storage pool composition is not limited to similar devices, but can consist of ad-hoc, heterogeneous collections of devices, which ZFS seamlessly pools together, subsequently doling out space to datasets (file system instances or ZVOLs) as needed. Arbitrary storage device types can be added to existing pools to expand their size. The storage capacity of all vdevs

9718-439: The hard disk drive. In Unix-like operating systems, many files have no associated physical storage device. Examples are /dev/null and most files under directories /dev , /proc and /sys . These are virtual files: they exist as objects within the operating system kernel. As seen by a running user program, files are usually represented either by a file control block or by a file handle . A file control block (FCB)

9831-418: The latter (afterwards deletion) method will have to only delete the files from the source directory that have already finished transferring. In modern computer systems, files are typically accessed using names ( filenames ). In some operating systems, the name is associated with the file itself. In others, the file is anonymous, and is pointed to by links that have names. In the latter case, a user can identify

9944-413: The name of the link with the file itself, but this is a false analogue, especially where there exists more than one link to the same file. Files (or links to files) can be located in directories. However, more generally, a directory can contain either a list of files or a list of links to files. Within this definition, it is of paramount importance that the term "file" includes directories. This permits

10057-550: The next 5 years. ZFS was ported to Linux , Mac OS X (continued as MacZFS ), and FreeBSD , under this open source license. The name at one point was said to stand for "Zettabyte File System", but by 2006, the name was no longer considered to be an abbreviation. A ZFS file system can store up to 256 quadrillion zettabytes (ZB). In September 2007, NetApp sued Sun, claiming that ZFS infringed some of NetApp's patents on Write Anywhere File Layout . Sun counter-sued in October

10170-414: The next write to the sector). This "silent correction" can be monitored using S.M.A.R.T. and tools available for most operating systems to automatically check the disk drive for impending failures by watching for deteriorating SMART parameters. Some file systems , such as Btrfs , HAMMER , ReFS , and ZFS , use internal data and metadata checksumming to detect silent data corruption. In addition, if

10283-402: The pathway from network to disk. Silent data corruption may result in cascading failures , in which the system may run for a period of time with undetected initial error causing increasingly more problems until it is ultimately detected. For example, a failure affecting file system metadata can result in multiple files being partially damaged or made completely inaccessible as the file system

10396-427: The physical disks and volumes (including their status, condition, and logical arrangement into volumes) as well as of all the files stored on them. ZFS is designed to ensure (subject to sufficient data redundancy ) that data stored on disks cannot be lost due to physical errors, misprocessing by the hardware or operating system , or bit rot events and data corruption that may happen over time. Its complete control of

10509-419: The pool are stored multiple times by default for safety even with the default copies=1 setting. If other copies of the damaged data exist or can be reconstructed from checksums and parity data, ZFS will use a copy of the data (or recreate it via a RAID recovery mechanism) and recalculate the checksum—ideally resulting in the reproduction of the originally expected value. If the data passes this integrity check,

10622-438: The pool less efficient. Free space in ZFS tends to become fragmented with usage. ZFS does not have a mechanism for defragmenting free space. There are anecdotal end-user reports of diminished performance when high free-space fragmentation is coupled with disk space over-utilization. Pools can have hot spares to compensate for failing disks. When mirroring, block devices can be grouped according to physical chassis, so that

10735-476: The pool. ZFS will also update its write strategy to take account of new disks added to a pool, when they are added. As a general rule, ZFS allocates writes across vdevs based on the free space in each vdev. This ensures that vdevs which have proportionately less data already, are given more writes when new data is to be stored. This helps to ensure that as the pool becomes more used, the situation does not develop that some vdevs become full, forcing writes to occur on

10848-658: The power supply might be unreliable, external vibrations such as a loud sound, the network might introduce undetected corruption, cosmic radiation and many other causes of soft memory errors , etc. In 39,000 storage systems that were analyzed, firmware bugs accounted for 5–10% of storage failures. All in all, the error rates as observed by a CERN study on silent corruption are far higher than one in every 10 bits. Webshop Amazon.com has acknowledged similar high data corruption rates in their systems. In 2021, faulty processor cores were identified as an additional cause in publications by Google and Facebook; cores were found to be faulty at

10961-470: The probability is much larger because they store much more data, whilst not being safer. That way, silent data corruption has not been a serious concern while storage devices remained relatively small and slow. In modern times and with the advent of larger drives and very fast RAID setups, users are capable of transferring 10 bits in a reasonably short time, thus easily reaching the data corruption thresholds. As an example, ZFS creator Jeff Bonwick stated that

11074-518: The purpose of a file at a glance. Some computer systems allow file names to contain spaces; others do not. Case-sensitivity of file names is determined by the file system . Unix file systems are usually case sensitive and allow user-level applications to create files whose names differ only in the case of characters. Microsoft Windows supports multiple file systems, each with different policies regarding case-sensitivity. The common FAT file system can have multiple files whose names differ only in case if

11187-513: The rules for how the bytes must be organized and interpreted meaningfully. For example, the bytes of a plain text file ( .txt in Windows) are associated with either ASCII or UTF-8 characters, while the bytes of image, video, and audio files are interpreted otherwise. Most file types also allocate a few bytes for metadata , which allows a file to carry some basic information about itself. Some file systems can store arbitrary (not interpreted by

11300-402: The same computer protects against failure of one disk, but if it is necessary to protect against failure or destruction of the entire computer, then copies of the files must be made on other media that can be taken away from the computer and stored in a safe, distant location. The grandfather-father-son backup method automatically makes three back-ups; the grandfather file is the oldest copy of

11413-513: The same year claiming the opposite. The lawsuits were ended in 2010 with an undisclosed settlement. Ported versions of ZFS began to appear in 2005. After the Sun acquisition by Oracle in 2010, Oracle's version of ZFS became closed source, and the development of open-source versions proceeded independently, coordinated by OpenZFS from 2013. Examples of features specific to ZFS include: One major feature that distinguishes ZFS from other file systems

11526-488: The storage device fall into the former category, while software failure typically occurs due to bugs in the code. Cosmic rays cause most soft errors in DRAM. Some errors go unnoticed, without being detected by the disk firmware or the host operating system; these errors are known as silent data corruption . There are many error sources beyond the disk storage subsystem itself. For instance, cables might be slightly loose,

11639-413: The storage stack and allow data corruption to occur while the data passes boundaries between the different layers. Data scrubbing is another method to reduce the likelihood of data corruption, as disk errors are caught and recovered from before multiple errors accumulate and overwhelm the number of parity bits. Instead of parity being checked on each read, the parity is checked during a regular scan of

11752-408: The storage system is used to ensure that every step, whether related to file management or disk management , is verified, confirmed, corrected if needed, and optimized, in a way that the storage controller cards and separate volume and file systems cannot achieve. ZFS also includes a mechanism for dataset and pool-level snapshots and replication , including snapshot cloning , which is described by

11865-509: The system can then update all faulty copies with known-good data and redundancy will be restored. If there are no copies of the damaged data, ZFS puts the pool in a faulted state, preventing its future use and providing no documented ways to recover pool contents. Consistency of data held in memory, such as cached data in the ARC, is not checked by default, as ZFS is expected to run on enterprise-quality hardware with error correcting RAM . However,

11978-482: The system is able to detect and correct the error; there is no data corruption in the latter case. Data corruption can occur at any level in a system, from the host to the storage medium. Modern systems attempt to detect corruption at many layers and then recover or correct the corruption; this is almost always successful but very rarely the information arriving in the systems memory is corrupted and can cause unpredictable results. Data corruption during transmission has

12091-611: The underlying hardware, rather than the contents stored on it, was denominated a "file". For example, the IBM 350 disk drives were denominated "disk files". The introduction, c.  1961 , by the Burroughs MCP and the MIT Compatible Time-Sharing System of the concept of a " file system " that managed several virtual "files" on one storage device is the origin of the contemporary denotation of

12204-580: The user uses a disk editor to edit the file names in the directory entries . User applications, however, will usually not allow the user to create multiple files with the same name but differing in case. Most computers organize files into hierarchies using folders, directories, or catalogs. The concept is the same irrespective of the terminology used. Each folder can contain an arbitrary number of files, and it can also contain other folders. These other folders are referred to as subfolders. Subfolders can contain still more files and folders and so on, thus building

12317-700: The usual read-modify-write sequence. As all stripes are of different sizes, RAID-Z reconstruction has to traverse the filesystem metadata to determine the actual RAID-Z geometry. This would be impossible if the filesystem and the RAID array were separate products, whereas it becomes feasible when there is an integrated view of the logical and physical structure of the data. Going through the metadata means that ZFS can validate every block against its 256-bit checksum as it goes, whereas traditional RAID products usually cannot do this. In addition to handling whole-disk failures, RAID-Z can also detect and correct silent data corruption , offering "self-healing data": when reading

12430-429: The way up the file system's data hierarchy to the root node, which is also checksummed, thus creating a Merkle tree . In-flight data corruption or phantom reads/writes (the data written/read checksums correctly but is actually wrong) are undetectable by most filesystems as they store the checksum with the data. ZFS stores the checksum of each block in its parent block pointer so that the entire pool self-validates. When

12543-402: The word. Although the contemporary " register file " demonstrates the early concept of files, its use has greatly decreased. On most modern operating systems , files are organized into one-dimensional arrays of bytes . The format of a file is defined by its content since a file is solely a container for data. On some platforms the format is indicated by its filename extension , specifying

12656-713: Was included in the mainstream 6/06 update to Solaris 10 . Solaris was originally developed as proprietary software , but Sun Microsystems was an early commercial proponent of open source software and in June 2005 released most of the Solaris codebase under the CDDL license and founded the OpenSolaris open-source project. In Solaris 10 6/06 ("U2"), Sun added the ZFS file system and frequently updated ZFS with new features during

12769-565: Was released under the name Solaris , which became the successor to SunOS 4 (although SunOS 4.1. x micro releases were retroactively named Solaris 1 ). ZFS was designed and implemented by a team at Sun led by Jeff Bonwick , Bill Moore, and Matthew Ahrens. It was announced on September 14, 2004, but development started in 2001. Source code for ZFS was integrated into the main trunk of Solaris development on October 31, 2005 and released for developers as part of build 27 of OpenSolaris on November 16, 2005. In June 2006, Sun announced that ZFS

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