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Re: Software Raid was ....Re: [K12OSN] HELP!!!

Hello Utsav,

RAID allows multiple simultaneous writes if you are using RAID 0,4,5.

The hardware RAID controller is the key to this. Because the data is
written to a drive stripe set, data is written across the set.

Below is a simple explanation of the concept.

EG. for RAID 0 (stripe set, no parity bit)

Drive1	Drive2	Drive3
bit1	bit2	bit3
bit4	bit5	bit6
and so on......

Therefore, when one byte of information is needed bits 1-3 would be read
simultaneously, then bits 4-6, and so on. The RAID controller would
assemble the bits into the byte of information needed.

That's why software RAID has a performance hit, because the server CPU
has to carry out this function.

Most hardware RAID controllers have their own processor that does this
job. Some early RAID controllers used the Intel 80186. Recent RAID
controllers I have seen tend to use a Motorolla processor.

So yes, a hardware raid controller should give a performance
improvement. That is a simple answer. There are a lot of other factors
which effect performance as well.


On Thu, 2002-12-05 at 03:33, Utsav Pardasani wrote:
> Is there a way RAID can increase the access time on a harddisk.
> Is there something like:
> Write same data to both drives at same time.
> Read different data from both disks simoultanieosly.
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