Can I add different size Z2 vdevs to an existing pool? e.g. I have a 10wide (8+2) Z2 vdev in the pool. Can I add another Z2 vdev (say 4+2) vdev to that pool. What I am reading on line says ‘no problem - as long as they are same TYPE, size is immaterial’. What my MSP is telling me is that the vdevs have to be identical in the pool. I’m looking for a ruling.. thanks
What is a (8+2) or (4+2)? is the +2 hot spares?
It is not recommended to mix the sizes as you will have odd performance impacts. If you have excellent back up, it would be better to make the pool into 2 VDEVS, each 8 wide, Raid-Z2. That’s if all the drives are the same size. You didn’t not mention your hardware specifics nor how this pool is used. It may end up okay if it is almost all reads and very little writes but it is unbalanced, otherwise.
Your MSP is incorrect, in terms of what’s required. It’s recommended that all vdevs be identical, in terms of number of drives, size of drives, and performance of drives (e.g., 5400 vs. 7200 vs. 10000 RPM), but none of those is required. Mismatched drive sizes, in particular, are very common; mismatched vdev widths are less common, but remain a valid configuration.
1 Like
used as a VEEAM backup repository. 8 data drives 2 parity drives. Individual DRIVES would have same specs as original. Only difference is quantity. Everything I’ve read up to this point says the vDEVs only need to be running the same RAID scheme (Z2 in this case) and they play fine with the original VDEV in a common pool.
Identical drives; size, speed, even manufacturer. Identifical Z2 RAID scheme. Only diff is the quantity under the vDEV.
I would not mix those two VDEVs due to performance. Another reason not to do it is I don’t think you can remove your desired, second VDEV from the pool while on Raid-Z(1,2,3). You would be stuck recreating the entire pool and VDEVs if this is just ‘temporary’. You might be able to add drives to the second VDEV but RAID-Zx-expansion comes with its own issues
Correct, only if every vdev in the pool is either a stripe or a mirror.
1 Like
Not sure why I would want to remove the 2nd VDEV. The idea is to feed additional drives into it over time to eventually get it up to the same size as the 1st VDEV. Its my understanding that RAIDZ expansion was ‘formalized’ with Electric Eel back in ‘24 allowing drives to be added ‘at will’
Correct, with the caveat that space reporting is borked (no fix!), and that you’ll lose a little on capacity compared with directly creating the vdev at its final width (fix is to rewrite all data, so probably not palatable).
For a backup pool with no particular performance requirements you may go ahead.