Re: Performance Impact of going from 2 parity drives to 4 parity drives in a 4-disk RAID set

No.

It's already a RAID 5, it will continue to be RAID 5.

Originally, it was a 3-disk RAID 5. Thus parity info was only on two disks.

We added a 4th disk, but the OS does not automatically change the
number of disks used for parity data.

If you were to create a 4 disk RAID 5 array from scratch, parity would
be spread across all 4 disks.

So the question is is it worth the trouble of going into DST to stop
and restart RAID 5 in order to get the OS to spread the parity across
all 4 disks instead of just 2 disks.

Charles

On Thu, Aug 21, 2008 at 3:17 PM, Raul A. Jager W. <raul@xxxxxxxxxx> wrote:

Are you changing from RAID 1 to RAID 5? RAID 5 usualy requires at least
3 drives to be usefull.

Charles Wilt wrote:

All,

related to my post about starting/stopping RAID....

The reason for stopping/starting RAID is to spread out the parity
information from the current 2 drives to all 4 drives in a 4-disk RAID
set.

However, one of the team members on the system admin team mentioned
that he was told, by IBM, there would be no noticable performance
impact of moving from 2 parity drive to 4 in a 4-disk RAID set.

Both of us find that surprising.

Does anybody have any first hand expirence to confim or deny this claim...

Thanks,

Charles Wilt

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