Garry T. Williams posted on Tue, 17 Dec 2013 23:12:25 -0500 as excerpted: > On 12-18-13 10:46:29 Anand Jain wrote: >> On 12/18/2013 10:03 AM, Garry T. Williams wrote: >> > I have been using btrfs for my /home partition on my home machine for >> > a few years now. I created the file system RAID1 using two disk >> > partitions. Recently I noticed btrfs fi df shows extra Data, System, >> > and Metadata allocations. >> >> this is a known bug in mkfs.btrfs, the workaround for now is to run >> balance on FS having some data. so that unused group- >> profile will go away. > > Thanks. > > garry@vfr$ sudo btrfs balance start /home > Done, had to relocate 50 out of 50 chunks > garry@vfr$ sudo btrfs filesystem df /home > Data, RAID1: total=22.00GiB, used=21.02GiB > System, RAID1: total=32.00MiB, used=12.00KiB > System, single: total=4.00MiB, used=0.00 > Metadata, RAID1: total=1.00GiB, used=419.60MiB > > Hmmm. > > Well, it's better, but the extra allocation for System is baffling. I > believe that this happened sometime after creating the file system. Keep in mind that btrfs remains under development, still improving old features and growing new ones as well as bugfixing (and of course unfortunately still adding new bugs with the new code occasionally, it comes with the development filesystem territory). Having seen the same thing happen here, I think the extra allocations were there all the time, but simply weren't originally reported. After some improvements in btrfs fi df, it more accurately reported the empty chunk-stub relics of mkfs.btrfs where it didn't before, so they appeared to be new even if they'd been there all the time. But a balance normally does remove them. Tho that doesn't explain why the balance didn't remove that 4 MiB single- mode system stub. It did on all my btrfs here. But I run gentoo and build/install gentoo's live-git btrfs-progs, and build/run the mainline development kernel from live-git as well, so I'm well into the 3.13-rcs by now, while you haven't even upgraded to 3.12 yet and are still on 3.11- stable series, which might account for that. Or perhaps another balance would kill the system-stub as well? I don't know. > Also balance on a RAID1 file system with exactly two drives doesn't make > much sense to me. Why would any "chunks" have to be relocated? I'm > clearly missing something here. You haven't read up on how btrfs balance works at the wiki, have you? Which means you're probably missing other information that might be helpful in administering your btrfs as well. It'll likely be worth your while to spend some time reading the user documentation there (and to bookmark it for further reference, too =:^) : https://btrfs.wiki.kernel.org/ For balance in particular, see: https://btrfs.wiki.kernel.org/index.php/FAQ#What_does_.22balance.22_do.3F Also of interest: https://btrfs.wiki.kernel.org/index.php/Balance_Filters Of course, the btrfs manpage is also useful. Basically, unless you limit it with the -d/-m/-s switches and/or filters, balance blindly rewrites/relocates every chunk on the filesystem, cleaning up and if applicable converting between redundancy types as it does so. So all chunks are relocated/rewritten. But the above documentation should also suggest trying this to see if it addresses that remaining single-mode system chunk stub: btrfs balance start -fsconvert=raid1 /home Especially if you're on spinning rust (not SSD), that should take quite a bit less time than a full balance as well, because you're only rebalancing the few MiB of system chunks, not the GiBs of data and metadata. Hopefully that'll kill the single-mode system stub-chunk. If not, you've probably hit a bug and should report it as such, tho you might wish to try it with the latest 3.12 stable or 3.13-rc first, in case the bug has already been fixed. -- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
