Recommended ZFS structure? Sharing pool with root vs. separate pool?

[candlerb (Brian Candler)]

@carschandler

Can I have my root file system on a ZFS pool and also have Incus use a dataset within that same pool as its storage device?

Yes. You can create an incus storage pool from an empty dataset within an existing pool. You don’t need to dedicate a whole zpool to incus.

@carschandler

Even if I can safely do this, is there some other reason it’s a bad idea?

It works fine for me, and I can’t see any reason not to do it. Most interesting settings are at the zfs dataset/zvol level. The zpool is where you configure your vdevs and hence replication (zmirror/raidz/dRAID), therefore if you have different replication requirements for your VMs then they’ll need to be in a different zpool. And you have to get ashift right, but things will suck badly if you don’t, and it usually picks the right value automatically.

@carschandler

Is there a specific ZFS recordsize that is preferred for Incus VMs?

I don’t have a simple answer to that, but note that recordsize can be set at the dataset level, so you don’t need to worry about it at the pool level, and you can tune it for different VMs.

@carschandler

Is this just saying that if you configured Incus at the zpool level, then it assumes ownership of the entire pool, so don’t maintain any other datasets/filesystems inside that pool? But if you configured Incus at the dataset level, it assumes ownership only over that dataset, so don’t use that dataset for other things, but it does not assume ownership over the entire zpool, so feel free to use it for other things?

Correct.