Karsten Vinding posted on Tue, 08 Jan 2019 20:40:12 +0100 as excerpted: > Hello. > > I have a Raid1 pool consisting of 6 drives, 3 3TB disks and 3 2TB disks. > > Until yesterday it consisted of 3 2TB disks, 2 3TB disks and one 1TB > disk. > > I replaced the 1TB disk as the pool was close to full. > > Replacement went well, and I ended up with 5 almost full disks, and 1 > 3TB disk that was one third full. > > So I kicked of a balance, expecting it to balance the data as evenly as > possible on the 6 disks (btrfs balace start poolname). > > The balance ran fine but I ended up with this: > > Total devices 6 FS bytes used 5.66TiB > devid 9 size 2.73TiB used 2.69TiB path /dev/sdf > devid 10 size 1.82TiB used 1.78TiB path /dev/sdb > devid 11 size 1.82TiB used 1.73TiB path /dev/sdc > devid 12 size 1.82TiB used 1.73TiB path /dev/sdd > devid 13 size 2.73TiB used 2.65TiB path /dev/sde > devid 15 size 2.73TiB used 817.87GiB path /dev/sdg > > The sixth drive sdg, is still only one third full. > > How do I force BTRFS to distribute the data more evenly across the > disks? > > The way BTRFS has done it now, will bring problems, when I write more > data to the array.
After doing the btrfs replace to the larger device, did you resize to the full size of the larger device as noted in the btrfs-replace manpage (but before you do please post btrfs device usage from before, and then again after the resize, as below)? I ask because that's an easy to forget step that you don't specifically mention doing. If you didn't, that's your problem -- the filesystem on that device is still the size of the old device, and needs resized to the larger size of the new one, after which a balance should work as expected. Note that there is very recently reported bug in the way btrfs filesystem usage reports the size in this case, adding the device slack to unallocated altho it can't actually be allocated by the filesystem at all as the filesystem size doesn't cover that space on that device. I thought the bug didn't extend to show, which would indicate that you did the resize and just didn't mention it, but am asking as that's otherwise the most likely reason for the listed behavior. I /believe/ btrfs device usage indicates the extra space in its device slack line, but the reporter had already increased the size by the time of posting and hadn't run btrfs device usage previous to that, and it was non-dev list regulars in the discussion that didn't know for sure and didn't have a replaced and as yet unresized-filesystem device to check, so we haven't actually verified whether it displays correctly or not yet. Thus the request for the btrfs device usage output, to verify all that for both your case and the previous similar thread... -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman
