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RAID 6 vs. RAID 5 + Hot Spare


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#1 Eli Johnson

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Posted 16 May 2007 - 02:54 PM

I'm setting up an 8 drive SATA array that will either be configured RAID 5 plus a hot spare or RAID 6, with each incorporating all 8 drives. The chassis and controller both will have an 8 drive capacity, so all bays and connections will be utilized. In either case, I likely won't keep an additional cold drive on hand, so consider that if there's a drive failure it will likely be a few days before I receive a replacement drive.

What would be the advantages of one setup over the other? The way I see it, I may as well use RAID 6, but maybe there's some reason to use RAID 5 with the hot spare.

#2 classical

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Posted 16 May 2007 - 08:37 PM

RAID-6 requires calculation of additional parity data and will therefore be slower. How much slower and whether this difference is really of any significance depends on how powerful the processor is on your RAID card.

However, RAID-6 offers additional redundancy in allowing for two simultaneous drive failures. Drive failures frequently are correlated and if you absolutely don't want to lose your data, this is the safer of the two options. There's always the possibility that a second drive will fail during the build of the hot spare.

#3 Rtech

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Posted 17 May 2007 - 12:22 PM

Other things to think about are the size of the array. If your RAID array is over a TB then RAID 6 is definitely a better choice because of the long rebuilding process. Also what if an unrecoverable read error occurs while the hot spare is rebuilding, in a RAID 6 environment the second set of parity can be used to continue rebuilding. So, it really comes down to how important is your data.

To add on performance loss RAID 6 has over RAID 5, Get a good hardware RAID controller like Areca to get the most out of RAID 6 and you’ll be good.

#4 Eli Johnson

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Posted 17 May 2007 - 07:31 PM

To add on performance loss RAID 6 has over RAID 5, Get a good hardware RAID controller like Areca to get the most out of RAID 6 and you’ll be good.


So one advantage that RAID 5 would have is better write performance? Makes sense. Can I assume the read performance of RAID 6 should be better given the added spindle?

#5 Olaf van der Spek

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Posted 18 May 2007 - 02:59 AM

To add on performance loss RAID 6 has over RAID 5, Get a good hardware RAID controller like Areca to get the most out of RAID 6 and you’ll be good.


So one advantage that RAID 5 would have is better write performance? Makes sense. Can I assume the read performance of RAID 6 should be better given the added spindle?

No and no.

#6 Big Buck Hunter

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Posted 18 May 2007 - 03:02 AM

The speed of RAID5 vs RAID6 is entirely dependant n the Controlers implementation of those two raid levels. Purchase a controller, bench both, go with the one that performs better.

Frank

#7 Eli Johnson

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Posted 18 May 2007 - 03:02 AM

No and no.

Care to elaborate?

#8 Eli Johnson

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Posted 18 May 2007 - 03:06 AM

The speed of RAID5 vs RAID6 is entirely dependant n the Controlers implementation of those two raid levels. Purchase a controller, bench both, go with the one that performs better.

I'm not really looking for the better perfomer. I was just curious about whether RAID 5 plus a hot spare might offer any advantages over RAID 6, whether it's in performance or some other aspect. As it stands, I'm planning on using RAID 6.

#9 Olaf van der Spek

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Posted 18 May 2007 - 07:09 AM

No and no.

Care to elaborate?

Actually, I might be wrong and it could be yes and yes. :)
If the controller also uses the parity, reads on RAID 6 could be faster because there's one extra drive.
Random writes are probably slower because it involves 6 accesses on 3 drives instead of 4 on 2.



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