The best practice for VNX2 hot spares is one spare for every 30 drives in your array. However, if you have a VNX2 on Flare 33 .051 release, you’ll notice that the “Recommended” default policy is 1 per 60.
This is a bug. There has been no change in the recommendations from EMC. If you want the policy to return to the recommended 1 per 30, you have to manually set it.
I noticed today when trying to do this via Unisphere that you can only set a 1 per 30 policy if you actually have 30 or more disks of a given type. If you have 6 EFD disks, your options through Unisphere are 1 hotspare per 2, 3, 4, 5, 6, or 60 disks. In order to set a 1 per 30 policy in this situation you must use navicli or naviseccli.
Get a list of the hotspare policy IDs:
navicli –h SPA_IP_ADDRESS hotsparepolicy –list
Set a policy ID to 1 per 30:
navicli –h SPA_IP_ADDRESS hotsparepolicy –set POLICY_ID_NUMBER –keep1unusedper 30 -o
Note that you only need to do this on SPA or SPB for each policy, not both.
I also wanted to quickly mention there isn’t a great danger in leaving this 1 per 30 because the hot spare policy is really only a reporting mechanism. E.g. if you leave the policy at 1 per 60, and you have 60 drives, and you have two hot spares with 58 used data disks, AND you have two drives fail….both spares will kick in. The hot spare policy does not control hot sparing behavior; it just reports compliance. (Actually it will also prevent you from creating a storage pool that would violate the hot spare policy, but only if you don’t manually select disks…)
But I still like having the hot spare policy reflect the recommended best practice, and that is still one hotspare for every 30 disks.
Information taken from: https://community.emc.com/thread/192199