10-09-2013, 03:37 PM
RAID Presentation
RAID Presentation.ppt (Size: 163.5 KB / Downloads: 91)
How RAID works
Raid is used to take multiple drives and have them virtualized as a single driver. All Raid structures contain one of two primary purposes: aggregated storage space or data redundancy. Both regular RAID and RAID 5 work the same way but what they can do is different.
Data redundancy
Your data can survive a complete failure of one hard drives, but if two drives fail at the same time, ALL data will be lost. Raid 5 array can actually still be used with one drive completely missing or not working. The data will then be rebuild on the fly. Recommended that you have a extra hard drive by your computer if this ever happens.
RAID 5
Raid 5 has a increased over head. This is the cost to the person for the extra hard drive that is taken up by the parity. If you have two hard drives and you want to have that much space available, you need to buy one more hard drive for parity.
Striping parity
Data is “striped” across the hard drives, with a dedicated parity block for each stripe. A, B, C and D represent data “stripes”. Each stripe vary in size from 4kb to 256kb per stripe. Stripes with a subscript P are the parity blocks. The parity is responsible for the data fault tolerance and is also the reason why you lose the amount of space equivalent to one drive
RAID performance
Raid 5, stores one file in three different hard drives. It then can be accessed in 1/3 the time. Because it will be read from all three drives. Each hard drive stores 1/3 of the file. This in a perfect situation, causes your read speed to be tripled – with even more performance potential in RAID 5 arrays containing additional hard drives. THE downfall is there is an increased overhead when writing to the drives caused by parity calculations.
RAID 10
RAID has levels 0-9, but you can add two single digit numbers to create a 2 digit number like RAID 1+0 to get Raid 10. Raid 10’s advantages are its very fast, it’s crash proof, and it eats disk space.For Raid 10 you need at least 2 physical hard drives. You also need a disk controller that’s understands RAID. Raid 10 works by striping and mirroring your data across at least two disks. Mirroring, or RAID 1, means writing your data to two or more disks at the same time.
History of raid
David A. Patterson led a team at the university of California, Berkeley that developed the idea of RAID storage. In 1987 Patterson said “We had just been working on RISC processors, and we consciously said, Processors are going to start getting fast, improving faster than they have in the past”. Patterson then had the graduate students think about ideas that were involved with the processes of making Processors faster.
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