Thanks for the reply, it's appreciated! > Mounting raid1 btrfs writable in degraded mode creates chunks with > single profile. This is long standing issue. What is rather surprising > that you apparently have chunk size 819GiB which is suspiciously close > to 10% of 8TiB. btrfs indeed limits chunk size to 10% of total space, > but it should not exceed 10GiB. Could it be specific Ubuntu issue? > > So when you wrote data in degraded mode it had to allocate new chunk > with "single" profile.
That's strange as I didn't write actual data to the disk during that time. Perhaps Ubuntu wrote some hidden file or something to it, I have no idea, but I didn't interact with the filesystem beyond doing the replace after mounting it. Still... 10% of 8TiB may be what's happening and if so that's really strange... and massive. I'd don't think it was a single chunk equal to 10% though, as when I converted it to raid1, I specified the soft filter with `-dconvert=raid1,soft`, and the resulting output once it was complete was: Done, had to relocate 825 out of 1648 chunks So the hypothesis that it was one large chunk doesn't make hold up to me knowing that output. I thus assume the chunks were all 1GiB given that many. Unfortunately I didn't save the output of the balance with `-dusage=0`, but I do recall it being in the 800s as well. > > Why didn't it free > > those up as it replaced the missing disk and duplicated the data in > > RAID1? > > Device replacement restored mirrored data (chunks with "raid1" profile) > on the new device. It had no reasons to touch chunks with "single" > profile because from btrfs point of view these chunks never had any data > on replaced device so there is nothing to write there. > > > Shouldn't it all be RAID1 once it's complete, > No. btrfs replace restores content of missing device. It is not > replacement for profile conversion. Makes sense, knowing that I would expect that. I just have no idea why it allocated 800GiB, especially since I didn't write anything to the single disk during the convert process, much less ~800GiB. > > Everything was RAID1 all up until the disk replacement, so it clearly > > did this during the `btrfs replace` process. > > No, it did it during degraded writable mount. > > > Did I do this wrong, or > > is there a bug? > > There is misfeature that btrfs creates "single" chunks during degraded > mount. Ideally it should create degraded raid1 chunks. Hmm... would be nice to see this then. Is there a patch for it, assuming it's planned? Thanks, -Jonah