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67-464: Sun 4/280 was a base system used for building an early RAID prototype. Models are listed in approximately chronological order. In 1989, Sun dropped the "Sun-4" name for marketing purposes in favor of the SPARCstation and SPARCserver brands for new models, although early SPARCstation/server models were also assigned Sun-4-series model numbers. For example, the SPARCstation 1 was also known as

134-475: A Samsung 970 EVO NVMe M.2 SSD (2018) with 1 TB of capacity has an endurance rating of 600 TBW. Recovering data from SSDs presents challenges due to the non-linear and complex nature of data storage in solid-state drives. The internal operations of SSDs vary by manufacturer, with commands (e.g. TRIM and the ATA Secure Erase) and programs like (e.g. hdparm ) being able to erase and modify

201-428: A cache (configurable as write-through or write-back ) for a conventional, magnetic hard disk drive. A similar technology is available on HighPoint 's RocketHybrid PCIe card. Solid-state hybrid drives (SSHDs) are based on the same principle, but integrate some amount of flash memory on board of a conventional drive instead of using a separate SSD. The flash layer in these drives can be accessed independently from

268-409: A live SD operating system are easily write-locked . Combined with a cloud computing environment or other writable medium, an OS booted from a write-locked SD card is reliable, persistent and impervious to permanent corruption. In 2011, Intel introduced a caching mechanism for their Z68 chipset (and mobile derivatives) called Smart Response Technology , which allows a SATA SSD to be used as

335-792: A vendor lock-in , and contributing to reliability issues. For example, in FreeBSD , in order to access the configuration of Adaptec RAID controllers, users are required to enable Linux compatibility layer , and use the Linux tooling from Adaptec, potentially compromising the stability, reliability and security of their setup, especially when taking the long-term view. Some other operating systems have implemented their own generic frameworks for interfacing with any RAID controller, and provide tools for monitoring RAID volume status, as well as facilitation of drive identification through LED blinking, alarm management and hot spare disk designations from within

402-550: A RAID 6 array will have the same chance of failure as its RAID 5 counterpart had in 2010. Mirroring schemes such as RAID 10 have a bounded recovery time as they require the copy of a single failed drive, compared with parity schemes such as RAID 6, which require the copy of all blocks of the drives in an array set. Triple parity schemes, or triple mirroring, have been suggested as one approach to improve resilience to an additional drive failure during this large rebuild time. A system crash or other interruption of

469-600: A constant average rate. The probability of two failures in the same 10-hour period was twice as large as predicted by an exponential distribution. Unrecoverable read errors (URE) present as sector read failures, also known as latent sector errors (LSE). The associated media assessment measure, unrecoverable bit error (UBE) rate, is typically guaranteed to be less than one bit in 10 for enterprise-class drives ( SCSI , FC , SAS or SATA), and less than one bit in 10 for desktop-class drives (IDE/ATA/PATA or SATA). Increasing drive capacities and large RAID 5 instances have led to

536-411: A constant power supply to retain data. DRAM-based SSDs are typically used in specialized applications where performance is prioritized over cost or non-volatility. Many SSDs, such as NVDIMM devices, are equipped with backup power sources such as internal batteries or external AC/DC adapters. These power sources ensure data is transferred to a backup system (usually NAND flash or another storage medium) in

603-471: A constant power supply. NAND flash-based SSDs store data in semiconductor cells, with the specific architecture influencing performance, endurance, and cost. There are various types of NAND flash memory, categorized by the number of bits stored in each cell: Over time, SSD controllers have improved the efficiency of NAND flash, incorporating techniques such as interleaved memory , advanced error correction, and wear leveling to optimize performance and extend

670-807: A controller, which manages the data flow between the NAND memory and the host computer. The controller is an embedded processor that runs firmware to optimize performance, managing data, and ensuring data integrity. Some of the primary functions performed by the controller are: The overall performance of an SSD can scale with the number of parallel NAND chips and the efficiency of the controller. For example, controllers that enable parallel processing of NAND flash chips can improve bandwidth and reduce latency. Micron and Intel pioneered faster SSDs by implementing techniques such as data striping and interleaving to enhance read/write speeds. More recently, SandForce introduced controllers that incorporate data compression to reduce

737-487: A dedicated RAID controller chip, but simply a standard drive controller chip, or the chipset built-in RAID function, with proprietary firmware and drivers. During early bootup, the RAID is implemented by the firmware and, once the operating system has been more completely loaded, the drivers take over control. Consequently, such controllers may not work when driver support is not available for the host operating system. An example

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804-462: A downside, such schemes suffer from elevated write penalty—the number of times the storage medium must be accessed during a single write operation. Schemes that duplicate (mirror) data in a drive-to-drive manner, such as RAID 1 and RAID 10, have a lower risk from UREs than those using parity computation or mirroring between striped sets. Data scrubbing , as a background process, can be used to detect and recover from UREs, effectively reducing

871-470: A few ways: Write hole is a little understood and rarely mentioned failure mode for redundant storage systems that do not utilize transactional features. Database researcher Jim Gray wrote "Update in Place is a Poison Apple" during the early days of relational database commercialization. There are concerns about write-cache reliability, specifically regarding devices equipped with a write-back cache , which

938-743: A limited lifetime number of writes, and also slow down as they reach their full storage capacity. SSDs also have internal parallelism that allows them to manage multiple operations simultaneously, which enhances their performance. Unlike HDDs and similar electromechanical magnetic storage , SSDs do not have moving mechanical parts, which provides advantages such as resistance to physical shock, quieter operation, and faster access times. Their lower latency results in higher input/output rates (IOPS) than HDDs. Some SSDs are combined with traditional hard drives in hybrid configurations, such as Intel's Hystor and Apple's Fusion Drive . These drives use both flash memory and spinning magnetic disks in order to improve

1005-864: A lower cost than pure SSDs. An SSD stores data in semiconductor cells, with its properties varying according to the number of bits stored in each cell (between 1 and 4). Single-level cells (SLC) store one bit of data per cell and provide higher performance and endurance. In contrast, multi-level cells (MLC), triple-level cells (TLC), and quad-level cells (QLC) store more data per cell but have lower performance and endurance. SSDs using 3D XPoint technology, such as Intel’s Optane, store data by changing electrical resistance instead of storing electrical charges in cells, which can provide faster speeds and longer data persistence compared to conventional flash memory. SSDs based on NAND flash slowly leak charge when not powered, while heavily-used consumer drives may start losing data typically after one to two year in storage. SSDs have

1072-477: A much faster rate than transfer speed, and error rates have only fallen a little in comparison. Therefore, larger-capacity drives may take hours if not days to rebuild, during which time other drives may fail or yet undetected read errors may surface. The rebuild time is also limited if the entire array is still in operation at reduced capacity. Given an array with only one redundant drive (which applies to RAID levels 3, 4 and 5, and to "classic" two-drive RAID 1),

1139-672: A particular Galois field or Reed–Solomon error correction . RAID can also provide data security with solid-state drives (SSDs) without the expense of an all-SSD system. For example, a fast SSD can be mirrored with a mechanical drive. For this configuration to provide a significant speed advantage, an appropriate controller is needed that uses the fast SSD for all read operations. Adaptec calls this "hybrid RAID". Originally, there were five standard levels of RAID, but many variations have evolved, including several nested levels and many non-standard levels (mostly proprietary ). RAID levels and their associated data formats are standardized by

1206-487: A redundancy mode—the boot drive is protected from failure (due to the firmware) during the boot process even before the operating system's drivers take over. Data scrubbing (referred to in some environments as patrol read ) involves periodic reading and checking by the RAID controller of all the blocks in an array, including those not otherwise accessed. This detects bad blocks before use. Data scrubbing checks for bad blocks on each storage device in an array, but also uses

1273-438: A second drive failure would cause complete failure of the array. Even though individual drives' mean time between failure (MTBF) have increased over time, this increase has not kept pace with the increased storage capacity of the drives. The time to rebuild the array after a single drive failure, as well as the chance of a second failure during a rebuild, have increased over time. Some commentators have declared that RAID 6

1340-936: A small amount of volatile DRAM as a cache, similar to the buffers in hard disk drives. This cache can temporarily hold data while it is being written to the flash memory, and it also stores metadata such as the mapping of logical blocks to physical locations on the SSD. Some SSD controllers, like those from SandForce, achieve high performance without using an external DRAM cache. These designs rely on other mechanisms, such as on-chip SRAM, to manage data and minimize power consumption. Additionally, some SSDs use an SLC cache mechanism to temporarily store data in single-level cell (SLC) mode, even on multi-level cell (MLC) or triple-level cell (TLC) SSDs. This improves write performance by allowing data to be written to faster SLC storage before being moved to slower, higher-capacity MLC or TLC storage. On NVMe SSDs, Host Memory Buffer (HMB) technology allows

1407-503: A specific fix. A utility called WDTLER.exe limited a drive's error recovery time. The utility enabled TLER (time limited error recovery) , which limits the error recovery time to seven seconds. Around September 2009, Western Digital disabled this feature in their desktop drives (such as the Caviar Black line), making such drives unsuitable for use in RAID configurations. However, Western Digital enterprise class drives are shipped from

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1474-601: A sudden power loss. Some consumer SSDs have built-in capacitors to save critical data such as the Flash Translation Layer (FTL) mapping table. Examples include the Crucial M500 and Intel 320 series. Enterprise-class SSDs, such as the Intel DC S3700 series, often come with more robust power-loss protection mechanisms like supercapacitors or batteries. The host interface of an SSD refers to

1541-735: A system in the same way as HDDs, SSDs are used in a variety of devices, including personal computers , enterprise servers , and mobile devices . However, SSDs are generally more expensive on a per-gigabyte basis and have a finite number of write cycles, which can lead to data loss over time. Despite these limitations, SSDs are increasingly replacing HDDs, especially in performance-critical applications and as primary storage in many consumer devices. SSDs come in various form factors and interface types, including SATA , PCIe , and NVMe , each offering different levels of performance. Hybrid storage solutions, such as solid-state hybrid drives (SSHDs), combine SSD and HDD technologies to offer improved performance at

1608-403: A write operation can result in states where the parity is inconsistent with the data due to non-atomicity of the write process, such that the parity cannot be used for recovery in the case of a disk failure. This is commonly termed the write hole which is a known data corruption issue in older and low-end RAIDs, caused by interrupted destaging of writes to disk. The write hole can be addressed in

1675-411: Is Intel Rapid Storage Technology , implemented on many consumer-level motherboards. Because some minimal hardware support is involved, this implementation is also called "hardware-assisted software RAID", "hybrid model" RAID, or even "fake RAID". If RAID 5 is supported, the hardware may provide a hardware XOR accelerator. An advantage of this model over the pure software RAID is that—if using

1742-482: Is RAID 0 (such as in RAID ;1+0 and RAID 5+0), most vendors omit the "+" (yielding RAID 10 and RAID 50, respectively). Many configurations other than the basic numbered RAID levels are possible, and many companies, organizations, and groups have created their own non-standard configurations, in many cases designed to meet the specialized needs of a small niche group. Such configurations include

1809-498: Is a caching system that reports the data as written as soon as it is written to cache, as opposed to when it is written to the non-volatile medium. If the system experiences a power loss or other major failure, the data may be irrevocably lost from the cache before reaching the non-volatile storage. For this reason good write-back cache implementations include mechanisms, such as redundant battery power, to preserve cache contents across system failures (including power failures) and to flush

1876-452: Is a data storage virtualization technology that combines multiple physical data storage components into one or more logical units for the purposes of data redundancy , performance improvement, or both. This is in contrast to the previous concept of highly reliable mainframe disk drives referred to as "single large expensive disk" (SLED). Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on

1943-490: Is also vulnerable to controller failure because it is not always possible to migrate it to a new, different controller without data loss. In practice, the drives are often the same age (with similar wear) and subject to the same environment. Since many drive failures are due to mechanical issues (which are more likely on older drives), this violates the assumptions of independent, identical rate of failure amongst drives; failures are in fact statistically correlated. In practice,

2010-584: Is booted, and after the operating system is booted, proprietary configuration utilities are available from the manufacturer of each controller. Unlike the network interface controllers for Ethernet , which can usually be configured and serviced entirely through the common operating system paradigms like ifconfig in Unix , without a need for any third-party tools, each manufacturer of each RAID controller usually provides their own proprietary software tooling for each operating system that they deem to support, ensuring

2077-496: Is infrequently changed (cold data) from heavily used blocks, so that data that changes more frequently (hot data) can be written to those blocks. This helps distribute wear more evenly across the entire SSD. However, this process introduces additional writes, known as write amplification, which must be managed to balance performance and durability. Most SSDs use non-volatile NAND flash memory for data storage, primarily due to its cost-effectiveness and ability to retain data without

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2144-419: Is only a "band aid" in this respect, because it only kicks the problem a little further down the road. However, according to the 2006 NetApp study of Berriman et al., the chance of failure decreases by a factor of about 3,800 (relative to RAID 5) for a proper implementation of RAID 6, even when using commodity drives. Nevertheless, if the currently observed technology trends remain unchanged, in 2019

2211-586: The Storage Networking Industry Association (SNIA) in the Common RAID Disk Drive Format (DDF) standard: In what was originally termed hybrid RAID , many storage controllers allow RAID levels to be nested. The elements of a RAID may be either individual drives or arrays themselves. Arrays are rarely nested more than one level deep. The final array is known as the top array. When the top array

2278-466: The magnetic storage by the host using ATA-8 commands, allowing the operating system to manage it. For example, Microsoft's ReadyDrive technology explicitly stores portions of the hibernation file in the cache of these drives when the system hibernates, making the subsequent resume faster. Dual-drive hybrid systems are combining the usage of separate SSD and HDD devices installed in the same computer, with overall performance optimization managed by

2345-463: The second-stage boot loader from the second drive as a fallback. The second-stage boot loader for FreeBSD is capable of loading a kernel from such an array. Software-implemented RAID is not always compatible with the system's boot process, and it is generally impractical for desktop versions of Windows. However, hardware RAID controllers are expensive and proprietary. To fill this gap, inexpensive "RAID controllers" were introduced that do not contain

2412-508: The SSD to use a portion of the system’s DRAM instead of relying on a built-in DRAM cache, reducing costs while maintaining a high level of performance. In certain high-end consumer and enterprise SSDs, larger amounts of DRAM are included to cache both file table mappings and written data, reducing write amplification and enhances overall performance. Higher-performing SSDs may include a capacitor or battery, which helps preserve data integrity in

2479-589: The Sun 4/60. This practice was phased out with the introduction of the SPARCserver 600MP series in 1991. The term Sun-4 continued to be used in an engineering context to identify the basic hardware architecture of all SPARC-based Sun systems. Sun 4/110, 4/150, 4/260 and 4/280 systems upgraded with the Sun 4300 CPU board (as used in the SPARCserver 300 series) were referred to as the 4/310 , 4/350 , 4/360 and 4/380 respectively. The Sun-4 architecture refers to

2546-724: The VME-based architecture described above and used in the Sun 4/100, 4/200, SPARCserver 300 and SPARCserver 400 ranges. Sun-4 support was included in SunOS 3.2 onwards and Solaris 2.1 to 2.4. OpenBSD and NetBSD also will run on the Sun-4 architecture families. Several variations on the Sun-4 architecture were subsequently developed and used in later computer systems produced by Sun and other vendors. These comprised: RAID RAID ( / r eɪ d / ; " redundant array of inexpensive disks " or " redundant array of independent disks " )

2613-450: The amount of data written to the flash memory, potentially increasing both performance and endurance. Wear leveling is a technique used in SSDs to ensure that write and erase operations are distributed evenly across all blocks of the flash memory. Without this, specific blocks could wear out prematurely due to repeated use, reducing the overall lifespan of the SSD. The process moves data that

2680-418: The bits of a deleted file. The JEDEC Solid State Technology Association (JEDEC) has established standards for SSD reliability metrics, which include: In a distributed computing environment, SSDs can be used as a distributed cache layer that temporarily absorbs the large volume of user requests to slower HDD-based backend storage systems. This layer provides much higher bandwidth and lower latency than

2747-446: The cache at system restart time. Solid-state drive A solid-state drive ( SSD ) is a type of solid-state storage device that uses integrated circuits to store data persistently . It is sometimes called semiconductor storage device , solid-state device , or solid-state disk . SSDs rely on non-volatile memory, typically NAND flash , to store data in memory cells. The performance and endurance of SSDs vary depending on

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2814-416: The chances for a second failure before the first has been recovered (causing data loss) are higher than the chances for random failures. In a study of about 100,000 drives, the probability of two drives in the same cluster failing within one hour was four times larger than predicted by the exponential statistical distribution —which characterizes processes in which events occur continuously and independently at

2881-426: The complete loss of the drive. Most of the advantages of solid-state drives over traditional hard drives are due to their ability to access data completely electronically instead of electromechanically, resulting in superior transfer speeds and mechanical ruggedness. On the other hand, hard disk drives offer significantly higher capacity for their price. In traditional HDDs, a rewritten file will generally occupy

2948-691: The computer like hard drives. In contrast, memory cards (such as Secure Digital (SD), CompactFlash (CF), and many others) were originally designed for digital cameras and later found their way into cell phones, gaming devices, GPS units, etc. Most memory cards are physically smaller than SSDs, and designed to be inserted and removed repeatedly. SSDs have different failure modes from traditional magnetic hard drives. Because solid-state drives contain no moving parts, they are generally not subject to mechanical failures. However, other types of failures can occur. For example, incomplete or failed writes due to sudden power loss may be more problematic than with HDDs, and

3015-593: The computer user, or by the computer's operating system software. Examples of this type of system are bcache and dm-cache on Linux , and Apple's Fusion Drive . The primary components of an SSD are the controller and the memory used to store data. Traditionally, early SSDs used volatile DRAM for storage, but since 2009, most SSDs utilize non-volatile NAND flash memory, which retains data even when powered off. Flash memory SSDs store data in metal–oxide–semiconductor (MOS) integrated circuit chips, using non-volatile floating-gate memory cells. Every SSD includes

3082-520: The data is still exposed to operator, software, hardware, and virus destruction. Many studies cite operator fault as a common source of malfunction, such as a server operator replacing the incorrect drive in a faulty RAID, and disabling the system (even temporarily) in the process. An array can be overwhelmed by catastrophic failure that exceeds its recovery capacity and the entire array is at risk of physical damage by fire, natural disaster, and human forces, however backups can be stored off site. An array

3149-509: The electrical resistance of materials in its cells, offering much faster access times than NAND flash. 3D XPoint-based SSDs, such as Intel’s Optane drives, provide lower latency and higher endurance than NAND-based drives, although they are more expensive per gigabyte. Drives known as hybrid drives or solid-state hybrid drives (SSHDs) use a hybrid of spinning disks and flash memory. Some SSDs use magnetoresistive random-access memory (MRAM) for storing data. Many flash-based SSDs include

3216-535: The event of an unexpected power loss. The capacitor or battery provides enough power to allow the data in the cache to be written to the non-volatile memory, ensuring no data is lost. In some SSDs that use multi-level cell (MLC) flash memory, a potential issue known as "lower page corruption" can occur if power is lost while programming an upper page. This can result in previously written data becoming corrupted. To address this, some high-end SSDs incorporate supercapacitors to ensure all data can be safely written during

3283-493: The event of power loss, preventing data corruption or loss. Similarly, ULLtraDIMM devices use components designed for DIMM modules, but only use flash memory, similar to a DRAM SSD. DRAM-based SSDs are often used for tasks where data must be accessed at high speeds with low latency, such as in high-performance computing or certain server environments. 3D XPoint is a type of non-volatile memory technology developed by Intel and Micron, announced in 2015. It operates by changing

3350-563: The factory with TLER enabled. Similar technologies are used by Seagate, Samsung, and Hitachi. For non-RAID usage, an enterprise class drive with a short error recovery timeout that cannot be changed is therefore less suitable than a desktop drive. In late 2010, the Smartmontools program began supporting the configuration of ATA Error Recovery Control, allowing the tool to configure many desktop class hard drives for use in RAID setups. While RAID may protect against physical drive failure,

3417-467: The failure of a single chip may result in the loss of all data stored on it. Nonetheless, studies indicate that SSDs are generally reliable, often exceed their manufacturer-stated lifespan and having lower failure rates than HDDs. However, studies also note that SSDs experience higher rates of uncorrectable errors, which can lead to data loss, compared to HDDs. The endurance of an SSD is typically listed on its datasheet in one of two forms: For example,

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3484-422: The following: Industry manufacturers later redefined the RAID acronym to stand for "redundant array of independent disks". Many RAID levels employ an error protection scheme called " parity ", a widely used method in information technology to provide fault tolerance in a given set of data. Most use simple XOR , but RAID 6 uses two separate parities based respectively on addition and multiplication in

3551-489: The following: The distribution of data across multiple drives can be managed either by dedicated computer hardware or by software . A software solution may be part of the operating system, part of the firmware and drivers supplied with a standard drive controller (so-called "hardware-assisted software RAID"), or it may reside entirely within the hardware RAID controller. Hardware RAID controllers can be configured through card BIOS or Option ROM before an operating system

3618-458: The growing personal computer market. Although failures would rise in proportion to the number of drives, by configuring for redundancy, the reliability of an array could far exceed that of any large single drive. Although not yet using that terminology, the technologies of the five levels of RAID named in the June 1988 paper were used in various products prior to the paper's publication, including

3685-469: The help of a third-party logical volume manager: Many operating systems provide RAID implementations, including the following: If a boot drive fails, the system has to be sophisticated enough to be able to boot from the remaining drive or drives. For instance, consider a computer whose disk is configured as RAID 1 (mirrored drives); if the first drive in the array fails, then a first-stage boot loader might not be sophisticated enough to attempt loading

3752-485: The lifespan of the drive. Lower-end SSDs often use QLC or TLC memory, while higher-end drives for enterprise or performance-critical applications may use MLC or SLC. In addition to the flat (planar) NAND structure, many SSDs now use 3D NAND (or V-NAND), where memory cells are stacked vertically, increasing storage density while improving performance and reducing costs. Some SSDs use volatile DRAM instead of NAND flash, offering very high-speed data access but requiring

3819-579: The maximum error rates being insufficient to guarantee a successful recovery, due to the high likelihood of such an error occurring on one or more remaining drives during a RAID set rebuild. When rebuilding, parity-based schemes such as RAID 5 are particularly prone to the effects of UREs as they affect not only the sector where they occur, but also reconstructed blocks using that sector for parity computation. Double-protection parity-based schemes, such as RAID 6, attempt to address this issue by providing redundancy that allows double-drive failures; as

3886-553: The number of bits stored per cell, ranging from high-performing single-level cells (SLC) to more affordable but slower quad-level cells (QLC). In addition to flash-based SSDs, other technologies such as 3D XPoint offer faster speeds and higher endurance through different data storage mechanisms. Unlike traditional hard disk drives (HDDs), SSDs have no moving parts, allowing them to deliver faster data access speeds, reduced latency, increased resistance to physical shock, lower power consumption, and silent operation. Often interfaced to

3953-648: The operating system without having to reboot into card BIOS. For example, this was the approach taken by OpenBSD in 2005 with its bio(4) pseudo-device and the bioctl utility, which provide volume status, and allow LED/alarm/hotspare control, as well as the sensors (including the drive sensor ) for health monitoring; this approach has subsequently been adopted and extended by NetBSD in 2007 as well. Software RAID implementations are provided by many modern operating systems . Software RAID can be implemented as: Some advanced file systems are designed to organize data across multiple storage devices directly, without needing

4020-741: The performance characteristics such as rotational latency and seek time . As SSDs do not need to spin or seek to locate data, they are vastly superior to HDDs in such tests. However, SSDs have challenges with mixed reads and writes, and their performance may degrade over time. Therefore, SSD testing typically looks at when the full drive is first used, as the new and empty drive may have much better write performance than it would show after only weeks of use. The reliability of both HDDs and SSDs varies greatly among models. Some field failure rates indicate that SSDs are significantly more reliable than HDDs. However, SSDs are sensitive to sudden power interruption, sometimes resulting in aborted writes or even cases of

4087-554: The performance of frequently-accessed data. Traditional interfaces (e.g. SATA and SAS ) and standard HDD form factors allow such SSDs to be used as drop-in replacements for HDDs in computers and other devices. Newer form factors such as mSATA , M.2 , U.2 , NF1 / M.3 / NGSFF , XFM Express ( Crossover Flash Memory , form factor XT2) and EDSFF and higher speed interfaces such as NVM Express (NVMe) over PCI Express (PCIe) can further increase performance over HDD performance. Traditional HDD benchmarks tend to focus on

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4154-690: The redundancy of the array to recover bad blocks on a single drive and to reassign the recovered data to spare blocks elsewhere on the drive. Frequently, a RAID controller is configured to "drop" a component drive (that is, to assume a component drive has failed) if the drive has been unresponsive for eight seconds or so; this might cause the array controller to drop a good drive because that drive has not been given enough time to complete its internal error recovery procedure. Consequently, using consumer-marketed drives with RAID can be risky, and so-called "enterprise class" drives limit this error recovery time to reduce risk. Western Digital's desktop drives used to have

4221-507: The required level of redundancy and performance. The different schemes, or data distribution layouts, are named by the word "RAID" followed by a number, for example RAID 0 or RAID 1. Each scheme, or RAID level, provides a different balance among the key goals: reliability , availability , performance , and capacity . RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole physical drives. The term "RAID"

4288-427: The risk of them happening during RAID rebuilds and causing double-drive failures. The recovery of UREs involves remapping of affected underlying disk sectors, utilizing the drive's sector remapping pool; in case of UREs detected during background scrubbing, data redundancy provided by a fully operational RAID set allows the missing data to be reconstructed and rewritten to a remapped sector. Drive capacity has grown at

4355-543: The same location on the disk surface as the original file, whereas in SSDs the new copy will often be written to different NAND cells for the purpose of wear leveling . The wear-leveling algorithms are complex and difficult to test exhaustively. As a result, one major cause of data loss in SSDs is firmware bugs. While both memory cards and most SSDs use flash memory, they have very different characteristics, including power consumption, performance, size, and reliability. Originally, solid state drives were shaped and mounted in

4422-638: The storage system would, and can be managed in a number of forms, such as a distributed key-value database and a distributed file system . On supercomputers, this layer is typically referred to as burst buffer . Flash-based solid-state drives can be used to create network appliances from general-purpose personal computer hardware. A write protected flash drive containing the operating system and application software can substitute for larger, less reliable disk drives or CD-ROMs. Appliances built this way can provide an inexpensive alternative to expensive router and firewall hardware. SSDs based on an SD card with

4489-536: Was invented by David Patterson , Garth Gibson , and Randy Katz at the University of California, Berkeley in 1987. In their June 1988 paper "A Case for Redundant Arrays of Inexpensive Disks (RAID)", presented at the SIGMOD Conference, they argued that the top-performing mainframe disk drives of the time could be beaten on performance by an array of the inexpensive drives that had been developed for

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