I am toying with the idea of adding a single 2TB SSD into an array of 15 8TB mechanical drives.  Basically, I'm looking to have access to a high-speed (for reads, anyway), parity-protected device.  I already have a 2 disk, 1 TB cache pool, but I would like to keep this disk out of that mix.

 

Is this a Bad Idea?  And if so, is an Unassigned  Device the way to go?

As long as you only need better read speeds it's fine, good idea to run a few parity checks after adding it (make sure after a few reboots also) to make sure the SSD garbage collection doesn't affect parity, it shouldn't.

6 hours ago, johnnie.black said:

As long as you only need better read speeds it's fine, good idea to run a few parity checks after adding it (make sure after a few reboots also) to make sure the SSD garbage collection doesn't affect parity, it shouldn't.

Thanks!  I'll give it a go (although my parity checks take in the 17 hour range these days).

 

I still haven't decided if this is going to work the way that I want, but I want to see this idea through, anyways.

For others reading along that may not realize what the OP does ... writes to the parity protected SSD will still be limited to the speed of the physical spinner parity drive(s). Reads will be as fast.

Interested in the potential use case for this?

 

edit: disregard, I misread this as ssd for parity.

Edited March 9, 20197 yr by tjb_altf4

I added a 1 TB SSD to my rig and used unassigned devices, passing it through directly to my Windows 10 Gaming VM.  Otherwise for array operations I use the caching, have 2 512GB nvme drives in a mirrored pair.  The only thing I keep on my array is media so playback from spinning disk is fine.