ABC OF RAID
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* What Is RAID?
RAID stands for Redundant Array of Inexpensive Disks.
RAID is a method of combining several hard drives into
one unit. It can offer fault tolerance and higher throughput levels than a
single hard drive or group of independent hard drives.
* Why Do We Need It?
RAID provides real-time data recovery when a hard drive
fails, increasing system uptime and network availability while protecting
against loss of data. Multiple drives working together also increase system
performance.
* Levels of RAID
| RAID Level | Description | Minimum # of Drives |
Benefit |
| RAID 0 | Data striping (no data protection) | 2 | Highest performance |
| RAID 1 | Disk mirroring | 2 | High data protection |
| RAID 0/1 | RAID 0 and RAID 1 combined | 4 | Highest performance with highest data protection |
| RAID 5 | Data striping with distributed parity | 3 + (hot spare optional) |
Best
cost/performance balance for multi-drive environments * Raid 5 useable storage= # of drives minus 1 drive minus hot spare |
* Compare The Types Of RAID Implementations
| Type | Description | Advantages |
| Software-based RAID | Included in
NOSs such as NetWare and Windows NT.® All RAID functions are handled by the host CPU which can severely tax its ability to perform other computations. |
* Low price. * Only requires a standard SCSI card |
| Hardware-based SCSI RAID Card | Processor-intensive RAID operations are offloaded from the host CPU to enhance performance. | * Data
protection and performance benefits of RAID. * Connectivity benefits of standard SCSI card. * More robust fault-tolerant features and increased performance versus software-based RAID |
| External Hardware RAID Card | Connects to the server via a standard SCSI card. RAID functions are performed on a microprocessor located in the external RAID storage subsystem. | * OS
independent ( Works with any OS). * Build super high-capacity storage systems for high-end servers |
RAID Glossary
|
Array Two or more hard disk drives grouped together to appear as a single device to the host computer. Cache A temporary, fast storage area that holds data from a slower storage device for quick access. Cache storage is normally transparent to the accessing device. Co-processor A processor that resides on an array that relieves the host CPU from executing processor-intensive operations such as RAID 5 parity calculations and secondary RAID 1 writes. Duplexing Mirroring across two RAID cards. Fault Tolerance The ability of a system to continue to perform its functions even when one or more hard disk drives have failed. Hot Spare A spare hard drive which will automatically be used to replace the failed member of a redundant disk array. Hot Swap The ability to remove a failed member of a redundant disk array and replace it with a good drive without bringing down the server or interrupting transactions that involve other devices. Mirroring (RAID 1) Provides data protection by duplicating all data from a primary drive on a secondary drive. NOS Network Operating System (i.e., NetWare, Windows NT server) Parity A form of data protection used by RAID level 5 to recreate the data of a failed drive in a disk array. RAID Levels Numbered 0 through 5, RAID levels refer to different array architectures that offer various advantages in terms of data availability, cost and performance. RAID levels 0, 1, 0/1, and 5 are the most popular. RAID 0 See "Striping" RAID 0/1 Combines RAID 0 (data striping) and RAID 1 (disk mirroring). RAID 1 See "Mirroring" RAID 5 Combines data striping (for enhanced performance) with distributed parity (for data protection) to provide a recovery path in case of failure. SCSI Stands for Small Computer System Interface. SCSI is the technology that allows you to connect various devices to your PC. This connection is made using a SCSI card that fits inside your computer. Striping (RAID 0) Spreads data evenly over multiple drives to enhance performance. Because there is no redundancy scheme, it does not provide data protection.
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