Re: RAID 6 rebuild time - can I slash it?

rob@xxxxxxxxx wrote on Thu, 20 Mar 2014 12:33:41 GMT:

Raid 6 would mean you'd have to lose at least two drives to be
wiped out. Raid 6 with hot spare means you'd have to lose at
least three drives, right?

Correct

Kind of like, which is better:
Raid 5 with a hot spare, or
Raid 6 with no hot spare
Either way, you'd have to lose two drives to be fried.

No, RAID6 you'd have to lose 3 drives to be fried.

With Raid 5 you lose the space of one drive to striping
(spread out across all drives). How much do you lose to Raid
6?

RAID6 has 2 parity stripes, so it's the equivalent of 2 drives.

Is there a performance degradation from removing one of your
disk drives of a 8 drive SCSI raid set to become hot spare?

I would say yes, there is likely to be a performance
degradation.

For SAS drives, you'll be chanGng from 8 drives with parity
striped across all & all available for use to 7 drives.

For SCSI drives, you'll be chanGng from 8 drives with parity
striped across all & all available for use to parity for 7
drives striped across only 4 of the 7.

In both cases, you can't use the hot spare and you have the
equivalent of 6 drives of capacity.

If you pick RAID6 instead, parity is striped across all 8
drives, you're using all 8 drives to support work while having
the equivalent of 6 drives worth of capacity.

I would think there would be two performance hits. One,
dropping from 8 drives supporting the raid stripe down to only
4. The other performance hit would be one less disk arm
assisting while it's just sitting there waiting to be hot
spare.

Agree.