Mixed VDevs?

[lasdem]

I have a pool with a RaidZ Vdev (3x12TB) and want to expand it with 2 additional disk (2x6 TB) which I want to have as a Mirror.
planned topology:

• Pool "hdd"
  • RaidZ1
    • 12TB
    • 12TB
    • 12TB
  • Mirror
    • 6TB
    • 6TB

I don't find the option in the UI to do this though.
If I go under "Manage Devices" and then "Add VDEV" I can add the 2 disks but end up with the Error "This type of VDEV requires at least 3 disks."
But I can't choose the type in this dialog.
If I click "Reset Layout" and add the disks it switches type to "Stripe", but thats also not what I want.

 

[winnielinnie]

It's absolutely supported in ZFS (although discouraged). Seems like in SCALE the GUI just outright "protects you from yourself" when it comes to mixing different vdev types under the same pool?

 

[NugentS]

What version?
I ask because shouldn't there be a force checkbox so you can do things that TN doesn't think are sensible?

Alternatively you can always do this in the command line - although there are some caveats about naming that you might like to look into (don't use /dev/sdd)

 

[lasdem]

What version?
I ask because shouldn't there be a force checkbox so you can do things that TN doesn't think are sensible?

Alternatively you can always do this in the command line - although there are some caveats about naming that you might like to look into (don't use /dev/sdd)

Hi, Sorry my version is TrueNAS-SCALE-22.12.0

If its possible via command line I will investigate further into it. Thanks

 

[HoneyBadger]

I'll see if I can look into this a bit.

As noted, using mixed vdev types is definitely not the "supported" or "encouraged" way to expand a pool - but a force/override might have been the intended method to allow it. The "Reset layout" defaulting to adding stripe vdevs is probably something that could result in the bad kind of "astonishment" as well.

 

[lasdem]

I know its not recommended, but since I have the disks like that I want to use them. And a separate pool for the 6TG mirror does not really seem useful to me, since I would prefer having one big pool for my smb share.
I could use it for a backup pool and backup my Windows PC to it, but nothing really worth backing up on that machine.
I also could use the mirror for other types of VDEV like Cache or LOG, but I am not sure if this is beneficial since they are also slow HDDs.

 

[HoneyBadger]

Definitely wouldn't be beneficial to add a slow spinning disk as a cache/log VDEV - those devices need to be significantly faster at random reads (cache) or synchronous writes (log) vs. your pool VDEVs to see a difference.

There's been some back-and-forth on this regarding whether or not the ability to force mismatched VDEVs should be exposed in the UI, if it should be possible through the use of an override option, or if it's best left as an entirely unsupported "here be dragons" method.

Similar to using partitions, it's possible to do it via ZFS the command line, and it does produce a warning dialog in the Storage dashboard:

However, the warning doesn't do justice to how dire of a situation one can put themselves in by making a habit of disregarding warnings and habitually clicking an "override" checkbox:

That pool has a RAIDZ1, a mirror, and a single-device stripe VDEV; and because of the presence of the Z1, neither of the latter two VDEVs can be removed, so pool redundancy is now reduced to "if sdg fails, so does the pool."