maandag, februari 28, 2005

Calculating the speed of harddisks (part 6)

What about Raid you might ask ?

Indeed, when you put a harddrive together with a couple of other drives, it
improves the performance. The best way, by far, is Raid. Some Raidlevels will give you better performance, while others improve security above all else.

Raid 0

Raid 0 is of course the most dangerous Raidset, and should be avoided in any situation where the data is critical. But when it comes to performance, it is the best there is. Multiply the speed of one disk, times the number of disks. If that number does not exceed the speed of your scsi bus, then you are smiling.

Raid 1 and 1+0

Raid 1 and 1+0 are often referred to as being the most expensive Raidsets. This is partly true, since you have to buy twice the number of HD's to get half the capacity. But they deliver outstanding performance.

consider this :

1 disk delivers 20MB/s. When configured in a mirror, the system is able to do "Split Seeks" which means that it can read from two disks at the same time. So 2 disks give you 40MB/s when reading. When writing, the speed will not go up, since everything has to be written twice. If your diskset performs 60 writes and 40 Reads, then you get 180 IO's. On a Raid 0 this would have been 100 IO's.. but on Raid 5, it would require 220 IO's -- I will clarify on a next installment. Cheers !

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