ZFS setup with

cmonty14

Cadet
Joined
Apr 13, 2021
Messages
1
Hi,

I'm new to TrueNAS and OpenZFS.
Before I continue with my ZFS setup I would like to clarify if my understanding is correct.

So, is it correct that a ZFS pool that consists of multiple vdevs, any vdev must be equal in
  • number of disks included in each vdev
  • RAID level
?

In case I have drives of different sizes (4TB, 2TB, 1TB), is it correct that a vdev should enclude only drives of the same size?

And what about partitions?
Would it make sense to include partitions (of the same size) of different drives in the same vdev?


THX for your replies.
 

sretalla

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Jan 1, 2016
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9,702
any vdev must be equal in
  • number of disks included in each vdev
  • RAID level
If you replace must with should in that statement, then you're right.

We would recommend that you do it like that, but for example, you may have a pool of 2 RAIDZ2 VDEVs where you also have a 3-way mirror of SSDs for a special/metadata VDEV.

Depending on your performance objectives, it may also make perfect sense to have RAIDZ2 VDEVs of differing sizes in the same pool... although with a pool for high IO, you wouldn't usually want to mix the site of any of the Mirrored VDEVs in the pool.

In case I have drives of different sizes (4TB, 2TB, 1TB), is it correct that a vdev should enclude only drives of the same size?
Yes, correct, should.

Any differently sized drives in the same VDEV will have their "excess capacity" (judged in comparison to the smallest drive in the VDEV) ignored anyway.

And what about partitions?
If you want to be supported in what you're doing, you assign entire disks.

Custom (and unsupported) work with the CLI can be done to have partitions participating in a pool... for folks who know what they are doing and are prepared to deal with the consequences of what they do.

Would it make sense to include partitions (of the same size) of different drives in the same vdev?
As already said, that's automatic (ignoring the excess)... and not recommended. But can make sense on your way to increasing all disks in the pool to the same size (which will automatically expand the pool to full size when the last disk reaches the full final size).
 
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