Performance, reliability and performance for file servers or other machines, where the storage of large or important files important. Disk drives are prone to error, though, and when they will fail written data is lost since the last backup. Hard drives have limitations on how fast they go, even though hard drive speed is only a constraint on the heavily loaded servers.
What is RAID?
You can get much greater capacity to avoid loss of data from disk failure, and do all thatreasonable cost using a technology called Redundant Array of Inexpensive Disks (RAID), invented at the University of California at Berkeley, by DA Patterson, G. Gibson and RH Katz. The industry uses the phrase redundant array of independent disks, so you likely to see both. RAID conventional hard drives with special host adapter change what data is on disk.
What is RAID
The idea behind RAID is to conventional hard drives in which personallyComputers and gang them together in parallel. The resulting assembly will give you the low cost of hard drives in high volume and high reliability, and produced a multiplier effect on the performance of individual disks.
) The host adapter (often as a controller in RAID systems) sits between a high-rate data stream (on the computer side and) some lower rate streams (on the hard disk on this page. When the computer writes to the disk, the host adapter high-rate data and breaks it into severalsynchronized streams, one for each disk, in a process called striping. The computer reads the host adapter lead to the fact that a data stream from each plate to take the set of multiplexed into a stream, and send the resulting stream to the computer.
Is shown in the example below, shares a high-speed stream in four separate hard drive data streams on the fourth installment of the combined stream.
There are six different levels of RAID functionality. The simplest RAID system, RAID level0, only stripes the data across multiple disks for better performance. There is no cost for redundant data storage and no protection against failure. The highest level is RAID 5, both striping for performance and redundancy for failure protection.
RAID Level 0
RAID level 0 spreads the data stream to multiple floppy disks. You can have a similar effect as RAID 0, by several hard drives and can in Windows 2000 or Windows XP use to simulateRAID in the OS. Assuming that your computer sends a sequence of data on a RAID-0-host adapter connected to two disks. The host adapters are the data to two drives Interleave, sending odd blocks on a disk, and even blocks on the other.
Since the data volume and speed of a floppy disk is a fraction of the aggregate, you get better power and performance of RAID 0 for a conventional hard drive. There is no error correction or redundant data is written to the array,But as RAID 0 can not survive a hard drive fails. They would RAID 0 is used only in situations where they needed the capacity or performance gains, but not the reliability of the data increases.
RAID Level 1
In the same way, RAID 0, only concentrating on capacity and performance with no concession to the reliability, RAID 1, focuses on dependable data retention with no concession to capacity or performance. RAID 1, also known as disk mirroring hard drives used in pairs, with two plates of a pair Savethe identical data. The redundant copy protects your data against hardware failures, but you're still vulnerable to user error when deleting important files.
Assuming that your computer sends a sequence of data on the RAID-1 host adapter connected to two disks. The host adapters are all the data you write to each of the two drives. The identical data is stored on both disks, so that when the data is not yet available. The process is completed when both drives have written the data, so that the writetake longer than
a record solely because of delays in non-synchronized rotation, and for I / O bus contention.
RAID 1 provides a higher reliability than RAID 0 or not conventional disk setups, it increases their power.
RAID Level 2, Level 3, Level 4
RAID 2 adds one or more disks to hold an error correction code can be reconstructed with the loss of data from a failed disk. When your computer sends a sequence of data on a RAID-2 host adapter, two relatedData from hard disks and a disk ECC, interleaving of the host adapter, the data for the two data disks. Odd blocks go on a
Drive, and also to the other. The host adapter calculates the error correction code for writing the data to the disk and writes it into the ECC drive.
RAID 3 is the same as RAID 2, except that it uses a simpler code - instead of ECC parity. RAID 3 has the same short-transfer performance limitations of RAID 2, but less memory overhead.
RAID 4 is almost the same asRAID 3, but instead of striping across disks at the byte level, it operates at the sector level. This makes RAID 4 like RAID 2 except that it uses parity rather than ECC, and it interleaves sectors. RAID 4 therefore has good data reliability and storage efficiency, as do RAID 2 and 3, and retains fast writes for large data blocks.
RAID Level 5
RAID 5 is the same as RAID 4, except that instead of dedicating a single disk to storing parity, the parity data stream is striped Suppose all the hard drives, your computer sends a sequence of data on a RAID 5 host adapter connected to four disks. The interleaving host adapter to ensure the data on the drives, that no one drive has two blocks of a group protected by a parity block.
The host adapter adds the new parity information in the data stream that it sends to the plate, mixing information in the parity with the initial data. As long as there is at least an additional hard drive than it originallyData streams, the loss of a hard drive can be only one data stream, and thus parity enough to regenerate the lost data.
Conclusion
RAID technology can be difficult to understand, especially for the beginner. Go through the tips above to understand, so you can make better purchasing decisions when creating your next computer system.
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