On Wed, Oct 30, 2013 at 12:15:16PM +0000, Mike Arnautov wrote: > I have just moved some partitions on two Linux (Mageia 3) boxes to > btrfs (call the boxes A and B). In both cases only a part of one > physical disk can be allocated to btrfs. > > On box A, the btrfs partition size is 419 GB and the resulting > usable space is 418 GB with 1GB reserved by btrfs for metadata. > > However, on box B, where the partition size is 388 GB, reserved > metadata amounts to 128 GB (!), leaving just 266 GB for data. > > I've now done box B twice. Once using btrfs-convert and once by > reverting to ext4, and using KDE control centre to change the type > of the partition to btrfs, restoring the data from backups. In both > cases metadata reservation amount to 128 GB -- about 30% of the > disk. > > Any suggestions on (a) what the cause might be and (b) how to > improve things? (a) Probably a kernel somewhere in the range 3.7-3.8 (possibly 3.6). These kernels had a problem with excessively overenthusiastic chunk allocation. If that's the case, a newer kernel should stop it happening again. Alternatively, you've got lots and lots of small (<3k) files, and it's decided to inline them all. (b) btrfs balance start -musage=5 /mountpoint should cleean up any little-used or empty chunk allocations, but on the kernels above, it'll probably overallocate again. You may need to bump the usage parameter up a bit (it's a percentage) to harvest more chunks, if the first run isn't sufficient. If you still have the problem, then send us the output of: btrfs fi show btrfs fi df /mountpoint uname -a and we can take another look at it. Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- All hope abandon, Ye who press Enter here. ---
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