Mixed VDEV Capacities?

TrueNAS General
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1

I did search the forum, but didn’t find anything that really would give an answer.

Scale 25.04.2.1
Existing pool: two mirror vdevs, 10tb and 8tb sata ‘nas’ drives

Found that I needed to add space, so I put in a pair of 3tb sas I have.

Storage → manage devices button for the pool → add vdev
Stepped through the menu, manually selecting the pair of 3tb drives.

Pool now shows a new mirror, space available increased, but now there is the “Mixed VDEV Capacities” warning. Investigated, found that somehow, I added a LOGS ‘device’ to the pool in addition to the new mirror.

zpool remove $pool $logs_device was run, and it successfully removed it, but the warning persists.

zpool status shows all three mirrors, partx shows the same partition sizes on the drives, pool devices show the same size on the devices list.

I’m at a loss as to why it’s complaining. Any ideas or things to look at?

2

This is nothing to worry about for many SOHO users.

The warning is simply telling you that your Data vDevs are quite a bit different in size. This can lead to irregular striping of new data. That means instead of striping the data across all 3 of your vDevs, ZFS might choose to stripe the data across only 2. Why ZFS selects such, is due to how much free space is available in each vDev.

Again, unless you are trying to get the best performance, this is of no concern.

3

Thank you for the info, the warning isn’t exactly clear as to why it appears. Is this documented somewhere? I did look, but very well could have missed it in the manual.

4

I don’t know if it is documented. Nor where any"official" explanation is located.