[SOLVED] Best use of a bunch of SSDs

[GeekVerve]

My Unraid implementation is intended to provide storage for media, documents and various workstation backups as well as host a few VMs for home lab use. My storage needs aren't all that huge. The 3x 4TB HDDs I have set up (1-parity and 2-pool) should be more than enough for quite some time. Over the years I've also accumulated a bunch of SSDs: 1-500GB, 4-256GB, 2-128GB, all SATA3, and I'm debating on how to use them.

 

My first thought was to dump them all into the cache pool and run all my VMs from there. I'm just not real keen on giving up half their capacity in doing so.

 

Then the idea occurred to me of using just the 4x 256GB drives for the cache pool and add the rest to the storage array. That would provide some fault tolerance and if it's not housing my VMs, 512GB should be plenty of write cache. I'm guessing that I could then set my VMs up to run from the SSDs in the storage array and turn off caching for those drives. Is that correct? Are there reasons this may not be a good idea?

 

What it boils down to is I'm trying to maximize the amount of fast SSD space available for VMs while still providing reasonable caching. Any suggestions or insights would be appreciated.

 

Edited May 14, 2020 by GeekVerve

[itimpi]

You definitely do not want the SSDs to be part of the array for several reasons:

• Trim is not supported for SSDs in the array
• Write performance would be badly compromised as the SSDs would be slowed down by the need to update parity on every write.

you may find that the best way to use SSDs that are not part of the cache is to use them as Unassigned Devices for use by VMs

[GeekVerve]

Yikes, completely forgot about the parity writes. I also didn't know trim is not supported in an array.

 

I hadn't considered using them as unassigned drives. That may be the way to go. Thanks!

 

[GeekVerve]

I've removed the 512GB and 2-128GB SSDs from the cache pool and formatted them as unassigned devices. I now have a couple VMs running quite happily on them. Thank you again for the advice.