On Mon, Jan 02, 2012 at 04:01:48PM +0100, Daniel Pocock wrote: > One thing I've already noticed in 2.6.39 (and both versions of the > tools) is that df results are misleading. E.g. if I run regular df (not > btrfs fi df), I am seeing the same amount of available space for all > filesystems. Is there currently a way to see space used by each > subvolume and snapshot and which kernel and tools versions might be needed? It's actually not possible in general. Since it's possible to have different bits of the FS (data vs metadata) with different replication levels, one byte written to the FS could take up either 1 or 2 bytes of raw disk storage, and there's no way of predicting what the overall usage will be, so it's not possible to give an accurate estimate of free space. Similarly, if you have a 10G subvolume, and a snapshot of it, then how much space does each one take up? If you said 10G, then you're wrong, because the total storage space for the two together is only 10G. If, on the basis of that, you said 5G each, you're wrong, because if you delete one of them, you get no free space back. If, on the basis of that, you said 0G each, you're wrong, because if you delete both of them you get 10G of free space back. The best you can ask is "if I delete this subvolume, how much space will I get back?", but even that's non-trivial: Arne Jansen is working on that feature as a side-effect of his quota work, and it will be coming at some point, but we can't do it right now. See the FAQ on filesystem usage[1] for how to interpret the btrfs tools for examining space usage, and the mis-named "sysadmin's guide"[2] for more horrible details of what's going on underneath. Hugo. [1] http://btrfs.ipv5.de/index.php?title=FAQ#Why_does_df_show_incorrect_free_space_for_my_RAID_volume.3F [2] http://btrfs.ipv5.de/index.php?title=SysadminGuide -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- I'm on a 30-day diet. So far I've lost 18 days. ---
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