The Pool is a Dynamic Pool.

Hi,

That would also be true for traditionnal pools.

For both pool types, probability is higher with 12+1 than 4+1. But two drives of the same raid set means DU, or worst DL if disks wont spin up again.

For dynamic pools, if the a RAID5 4+1 choice means a DU when 2 disks amongst 200 (for example) fail at the same time, that is a risky option.

I have experience with VNX, and always prefer to use raid 4+1 in traditional pools. A pool with 20 disks would have 4 internal raids, so it could be possible to loose more than one drive as loong as they belong to different raid group.

But now I am planning to by a 450F with 20 1,6TB ssd, and I am not sure what configuration select:

- 1 dynamic pool with 20 disks (23,5 TB)

- 2 dynamic pools with 10 disks (21,7TB)

I am worried about the fact of loosing more than one drive at the same time.

a LUN isnt restricted to one raidgroup

if you want to be protected against dual drive failue than you should use RAID6

The problem for raid6 will be the performance. It is not recommended.

That is the reason for me to consider 2 different pools.

The question is that if I create a traditional pool with 20 disks, I can choose raid5 4+1 and could (potentially) tolerate 4 failed disks. With dynamic pool, it internally create one isolation domain every 64 disks, so for me it seems more probable 2 failures in 64 disks thant 2 failures in 5 disks.

I suppose that EMC should have a good explanation for doing this, but I cannot find it. Even xtreamio uses somethink like raid 6.