P4500G2 Hardware RAID Level

[Patrick Neuner]

Hello,

we are just installing our first P4500 and I got a little Question about the Hardware RAID Level.

The P4500 comes with 2 x RAID 5 per node.

I was wondering if it would be better (performance wise) to make 1 large RAID 5 spanning all 12 disks?

Are there any downsides doing this?

Thank you

Andreas

[Johan Guldmyr]

Hi, there's some math and statistics behind why having a RAID5 on a 12 disk array. 

http://www.miracleas.com/BAARF/ has some subjective posts that explain some of the statistics involved.

You may want to investigate if RAID6 is a possibility. If so, does that make a performance difference?

Does a larger RAID6 array have a longer rebuild time than 2 RAID5?

[oikjn · Accepted solution]

stay away from a 12-dirsk raid5 group.  the rebuild time will be so long that there is a high likelyhood of an unrecoveralbe data loss before the rebuild is complete.  The benefit of getting that 1/12th extra space is never worth the risk.

I don't have the time to find the link, but google did a large study on sibling mortality rates and found that drives produced together in the factory tended to fail together in the field when subjected to similar loads.  Short story is that when one disk fails, there is an even higher chance that another disk will fail if all the disks were purchased togther.

Use raid6 if you really want one large span, but ask yourself why...  HP decided on the two raid5 over one large array for a reason.