How bad is the failing disk? You could add the 12TB disk, have a 3 disk mirror, then when the 12 TB disk is written remove the failing disk. You could even do it all together as a 4 disk mirror if you have both 12TB disks.
Otherwise what you’re suggesting makes sense. My VM array (3 way mirror of SSDs) has gone through 2 rounds of a similar process.
The failing disk have hundreds of checksum errors, so I guess pretty bad. I’m still wondering whether I should just offline it at this stage or keep it going. I’ve replicated the dataset that sits on this pool on another healthy pool anyway, and I’ve done this after I saw that the disk is failing.
That’s exactly the way it works, once you click the “expand pool” button. iX broke pool auto-expansion in SCALE and have decided “we meant to do that.”
On 25.10 I saw my raidz2 pool space automatically grow after replacing a 6tb drive with a 12tb drive. The same should happen as long as you replace the drives directly and not create another another vdev
On 25.10.2.1 - Goldeye Date 5/5/2026 I tried to do the same thing, finished resilvering 2x2TB HDDs with 2X22TB HDDs one by one with the “Replace” button in the same vdev.
after finishing, under Storage the vdev tab shows 22TB or 20.01TiB, but under Usage tab it still shows 82.9% usage for 1.46 TiB used meaning that the vdev recognizes both new HDDs and the pool is online but for some reason the pool does not expand automatically as described. no “Expand” button available.
after restart that took unexpectedly long to complete, “Expand” button shows up under Storage tab, after pressing it, Dataset update to show apropriate available space, but under the Storage Usage usage is still reported as 80%.
5 minutes later updated to the apropriate precentage considering the new capacity, probably delay due to some delayed poling in the background?
