A RAID controller cards may be a card or chip set between the software package and therefore the storage drives, usually magnetic disk drives. RAID provides data redundancy and/or improves hard disk drive performance; most RAID levels do both. RAID does offer redundancy on SSDs, however doesn’t improve SSD performance. The RAID factory-made specifically for SSDs can provide redundancy and improve performance.
RAID controllers work by virtualizing the drives into distinct teams with specific information protection and redundancy characteristics. The front-end interface communicates with the server, typically via a host-based adapter (HBA) and therefore the backend communicates with and manages the underlying storage media; usually ATA, SCSI, SATA, SAS, or Fibre Channel.
RAID controllers are classified by multiple characteristics as well as drive sorts similar to SATA or SAS, the quantity of ports and number of drives it will support, specific RAID levels, interface architecture, and the way abundant memory exists in native cache. For example, this suggests that a controller factory-made for a SATA atmosphere won’t work on a SAS array, whereas a RAID one controller can not be changed into a RAID 10.
The form RAID stands for redundant array of freelance disks. A RAID system could also be hardware or software, and virtualizes physical storage drives to enhance performance and make information redundancy. Controller-based RAID typically refers to hardware-based RAID, as against server-based RAID, that is each software-defined and software-hardware hybrids.
RAID controllers don’t seem to be storage controllers. Storage controllers present active disks to the OS, whereas the RAID controller acts as a RAM cache and provides RAID functionality. The quantity and identity of RAID disks depends on a RAID controller’s configuration.
Hardware-Based: RAID Controller
Dedicated hardware managementlers are available in 2 totally different architectures:
An external RAID Controller Card and an inside RAID-on-Chip:
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RAID Controller Card:
A RAID controller card may be a plug-in enlargement card that connects to a PCIe or PCI-X motherboard slot. It contains a RAID processor and I/O processors with drive interfaces.
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RAID-on-Chip:
Less costly RAID-on-Chip is a single motherboard chip that integrates the host interface, HDD I/O interfaces, the RAID processor, and a memory controller. computer code begins RAID throughout bootup, then transfers control to the drivers.
Software-Based: Server-Based RAID
Software RAID delivers RAID services from the host. It comes in 2 flavours:
Software-defined hosted within the OS, associated with a hybrid design that contains a hardware part to alleviate the load on the CPU.
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Software-only RAID:
Software-only RAID is sometimes enclosed as a native operating system on the OS, which makes it the smallest amount of the RAID options. The host-based application manages RAID calculations, and attaches to the storage drives exploitation an HBA or native I/O interface. It starts up once the OS sends the RAID driver.
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Hybrid hardware/software RAID:
Hybrid hardware/software RAID uses a hardware component to deliver RAID BIOS functions from the motherboard or HBA. The hybrid technology adds another layer and is dearer than the software-only. However, it protects the RAID system from boot errors ought to one thing happen to the operative system.
What are the various RAID Levels?
See this in-depth discussion of RAID levels. Here’s a summary:
RAID controllers are specific to RAID levels. the foremost common levels are RAID zero, 1, 5/6, and 10. For additional in-depth information, scan RAID Levels.
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Raid 0:
Striping: RAID 0 is that the solely RAID level that doesn’t offer redundancy, but only will increase magnetic disk performance. RAID zero splits files and stripes the information across 2 disks or additional, treating the patterned disks as one partition. Since it treats multiple disks as a single partition, if even one drive fails, the striped file is unreadable. Usage case: HDD performance improvement solely; no data redundancy.
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RAID 1:
Mirroring: RAID 1 works on two or more desks to produce data redundancy and failover. It reads and writes the precise same data to every disk. ought to a reflected disk fail, the file exists in its totality on the functioning disk. Once the failed table is repaired or replaced, the RAID system can mechanically mirror information back to the replacement drive. RAID one additionally will increase scan performance. Usage case: information redundancy and quicker reads at an occasional cost.
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Raid 5/6:
Marking with Parity/Double Parity: RAID 5/6 combines the performance of RAID zero with the redundancy of RAID 1, however needs regarding tierce of usable capacity. “Parity” refers to raw binary data. RAID 5 stripes data across 2 or additional disks, and calculates block-level values to form a parity block. RAID 5 stores dedicated parity blocks on patterned HDD. ought to a drive fail, RAID five uses its dedicated parity block to construct information on the remaining nodes. The RAID half dozen operates like RAID 5 however needs a minimum of 4 disks in the associate array, thus it will store an extra parity block on every HDD. This ends up in an extremely out there configuration wherever 2 disks might fail before the array becomes unavailable. Usage case: internet servers, intensive scan environments, application servers, massive storage arrays.
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RAID 10:
Marking and Mirroring: RAID 10 is the costliest of the RAID levels. It stripes across a minimum of four disks for higher performance, and mirrors for redundancy. In a four-drive array, the system stripes information to 2 of the disks. The remaining two disks mirror the patterned disks, all storing half the data. Usage case: high security and superior environments similar to intensive transactional databases storing sensitive information. RAID ten is that the costliest RAID level for HDDs, however offers high scan and write speeds additionally as sturdy data redundancy.
Advantages of RAID:
RAID may be an elementary data protection and driver for HDD and SSD, and a performance driver for HDD. prime advantages include:
- Higher reliability: Except for RAID 0, RAID ensures that one crashed node won’t take an associated array down with it. Applications still operate remaining nodes whereas the failing node is repaired or replaced. That maintains information consistency and guards against data loss.
- Information redundancy: RAID mirroring and/or marking with parity spreads data across multiple nodes, guaranteeing that no data is lost ought to a node fail.
- Higher HDD performance: Most RAID levels improve outturn by permitting applications to at the same time scan and write data from multiple drives. This is often not an automatic improvement: higher RAID levels, particularly RAID 10, take up system overhead, creating them unsuitable for low or mid-performance arrays. These arrays profit most from RAID performance improvement, or RAID 5/6 for performance and redundancy. On a superior array, RAID ten will increase performance and provide redundancy and high availability.
Disadvantages of RAID Controllers:
The controller design of hardware-based RAID is dearer than software-based RAID, however increases system performance and isn’t also subject to errors.
- Cache memory: Controller-based RAID typically provides extra dick cache memory that accelerates RAID operations.
- Dedicated processing: Controller-based systems severally manage RAID configuration aside from the OS. And since the RAID controller doesn’t need disk process power, capability and speed win out over software-only RAID.
- Lack of boot errors: And since software-only RAID is found on the OS, it’s also subject to errors which will comprise a complete array. Boot errors won’t have an effect on RAID controllers.
- Not every atmosphere is sensible for controller-based RAID. In a very tightly budgeted storage environment, software-only RAID zero will improve HDD performance and software-only RAID one will offer acceptable information redundancy.
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