On Mon, Oct 15, 2018 at 05:40:40PM +0300, Anton Shepelev wrote: > Hugo Mills to Anton Shepelev: > > >>While trying to resolve free space problems, and found > >>that I cannot interpret the output of: > >> > >>> btrfs filesystem show > >> > >>Label: none uuid: 8971ce5b-71d9-4e46-ab25-ca37485784c8 > >> Total devices 1 FS bytes used 34.06GiB > >> devid 1 size 40.00GiB used 37.82GiB path /dev/sda2 > >> > >>How come the total used value is less than the value > >>listed for the only device? > > > > "Used" on the device is the mount of space allocated. > >"Used" on the FS is the total amount of actual data and > >metadata in that allocation. > > > > You will also need to look at the output of "btrfs fi > >df" to see the breakdown of the 37.82 GiB into data, > >metadata and currently unused. > > > >See > >https://btrfs.wiki.kernel.org/index.php/FAQ#Understanding_free_space.2C_using_the_original_tools > > for the details > > Thank you, Hugo, understood. mount/amount is a very fitting > typo :-) > > Do the standard `du' and `du' tools report correct values > with btrfs?
Well... du will tell you the size of the files you asked it about, but it doesn't know about reflinks, so it'll double-count if you've got a reflink copy of something. Other than that, it should be accurate, I think. There's also a "btrfs fi du" which can tell you the amount of shared and unique data as well, so you can know, for example, how much space you'll reclaim if you delete those files. df should be mostly OK, but it does sometimes get its estimate of the total usable size of the FS wrong, particularly if the FS is unbalanced. However, as the FS fills up, the estimate gets better, because it gets more evenly balanced across devices over time. Hugo. -- Hugo Mills | "Your problem is that you have a negative hugo@... carfax.org.uk | personality." http://carfax.org.uk/ | "No, I don't!" PGP: E2AB1DE4 | Londo and Vir, Babylon 5
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