Volumes and nvme caches


Firstly - thanks for all the content!

Just setting up a new unit and trying to plan a little especially as i first of all whacked one volume across the RAID6 ~40TB storage pool and went to add a cache (2 * 750GB nvme, raid 1) which initially warned about the cache raid not being to the same level as the pool and then also warned (for read write with the brtfs pinned) that i should have 2% of the volume size (i.e. ~800GB)

Realistically the cache is probably only going to make a noticeable difference for my usage type for up to 10TB of the data within the next couple of years.

So - i intend to create a couple of volumes including one of 10TB which i’ll assign the cache to.

My question(s) i’d prefer to know without having to create to test…

  1. Can the cache be assigned to more than one volume in a pool - i’m assuming it will be restricted to only volumes assigned
  2. What happens if you increase a volume size where a cache has been assigned - is the cache entirely independent or will it want to recreate it (provided i’m not asking it to cache for a vastly bigger capacity volume - i.e. greater than that 2%)

Hope those questions make sense!



Hi Andy,
Some brief answering my own experience.

  1. Yes
  2. I do not know

Cheers Paul - i might try before it’s got any data on to find out… will report back