Should domains share be on the cache or in the pool? And why?

[wayner]

I have two VMs - Ubuntu and Win11.  A few weeks ago I had mover move the files off my cache to the pool to reformat my cache drive to ZFS and add a second disk to the pool in a mirrored configuration.

 

I just noticed that my domains share is mainly in the pool - when I look at the config for the domains share I forgot to change the mover action back to Pool->Cache, it is at Cache->Pool.  But my VMs seem to be working ok and don't seem to be much slower, although I haven't used them a lot.

 

I tried googling and don't see a clear answer - what is the reason to have domains on cache?  Is it because a VM will run a lot faster on my cache which is a NVME disk, compared to the pool which are regular hard drives?

[bmartino1]

You want the VM on the faster drive for performance as there are more reads then writes in a VM.

 

It comes down to how you handle your drives and the configuration what type of drives are setup for your array and parity.

 

I run a nvme cache drive.

1tb hdd disk 1 no parity 

 

And 3x 16 tb chach ZFS raidz1 pool

 

I default to missing the NVME for performance. Dockers and VM.

[wayner]

I have two 500GB NVME SSDs in a mirrored ZFS pool for my cache and several 4GB or larger spinning hard drives in my array.  I would think that the NVME would be faster.

[itimpi]

14 hours ago, wayner said:

back to Pool->Cache, it is at Cache->Pool.

Something not quite right in your explanation as mover direction can only be to/from array.

[wayner]

Sorry, I was using the wrong terminology.  The current setting is Cache->Array. I did that to clear off my cache disk to reformat it, and did the same with other shares like appdata, system, etc.  But I guess I forgot to change the setting back to Array->Cache for the domains share.

[trurl]

Ideally, appdata, domains, system share would all be on fast pool such as cache, with no files for those shares on the array. This will help Docker/VM performance, and allow array disks to spin down since these files are always open.

 

You can see how much of each disk is used by each share by clicking Compute... for the share on the User Shares page.

 

Note that nothing can move open files, so if you need to move these to cache, you will have to disable Docker and VM Manager in Settings.