Mixed disk size VDEV - replace disk question

[GBillR]

I feel as if I should know the answer to this, and I have searched the forums and the resource docs to no avail... apologize if I missed the answer to my question elsewhere. I would like to test this out, but have no easy way to do that at the moment...

Hypothetically speaking, if I have a pool with a single VDEV of mixed size disks... something like 5x2TB and 3X4TB in a Z2, I know that the VDEV is limited in size by the smallest disk.

I also know that you cannot replace a disk with a smaller disk, as explained everywhere. But what I've not seen anyone specifically ask is this: Since the VDEV is limited in size based on the smallest disk, is it possible to replace one of the 4TB disks with a 2TB disk in this VDEV? My instincts tell me "no", but it also seems to me like it should be possible...

I await the scolding and the schooling that will accompany it.

Thank you!

 

[Whattteva]

It's a really interesting question. I'd say the answer is probably no, but someone with more knowledge should chime in.

 

[danb35]

I'd say the answer is probably yes, but I can't say that I've tried it to be sure.

 

[GBillR]

It's a really interesting question. I'd say the answer is probably no, but someone with more knowledge should chime in.

I'd say the answer is probably yes, but I can't say that I've tried it to be sure.

I am relieved that I have not asked a completely dumb question... I'll wait a few days to see if someone knows the answer to this before I do my own testing. I would have to do some creative drive shuffling to try it out on my current hardware.

 

[Whattteva]

I am relieved that I have not asked a completely dumb question... I'll wait a few days to see if someone knows the answer to this before I do my own testing. I would have to do some creative drive shuffling to try it out on my current hardware.

@danb35 is probably correct and you can probably downgrade as long as the vdev was created with at least 1x 2TB drive. You probably just have to replace and resilver the drive.

 

[Arwen]

@GBillR Interesting question. I thought about that too, but have had no opportunity to either try it, or get a definitive answer.

If you try it, let us know the results.

 

[GBillR]

It's a really interesting question. I'd say the answer is probably no, but someone with more knowledge should chime in.

I'd say the answer is probably yes, but I can't say that I've tried it to be sure.

Interesting question. I thought about that too, but have had no opportunity to either try it, or get a definitive answer.

If you try it, let us know the results.

So the answer to my question is yes. I tested this with a pool consisting of a single vdev of 7x2TB. As I was upgrading the disks to 3TB, I went ahead and attempted to take one of the replaced 2TB drives, wipe it, and then use it to replace one of the 3TB drives I had already used to upgrade. The 2TB happily replaced the 3TB drive.

Mind you, I had not yet completed the replacement of all 7 disks. Once I replace the last of the 2TB disks in the vdev, I am certain that there will be no going back. This gives me something to think about now. I have 7 of each of these 2 and 3 TB drives laying around, and I am really in no need for the space... I was just using it to keep my main storage pool under 60% These 2 and 3 TB drives are pretty old... a couple are over 50k hours. Perhaps keeping the vdev from "expanding" gives me more flexibility when these old drives finally kick. Since I won't have an extra spare 3TB drive laying around if I use all 7 in upgrading this pool. Guess I need to think about it... but at least I know I have more options now.