Re: Interpreting `btrfs filesystem show'

[Martin Steigerwald <martin@lichtvoll.de>]

Hugo Mills - 15.10.18, 16:26:
> On Mon, Oct 15, 2018 at 05:24:08PM +0300, Anton Shepelev wrote:
> > Hello, all
> > 
> > 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.

I usually use btrfs fi usage -T, cause

1. It has all the information.

2. It differentiates between used and allocated.

% btrfs fi usage -T /
Overall:
    Device size:                 100.00GiB
    Device allocated:             54.06GiB
    Device unallocated:           45.94GiB
    Device missing:                  0.00B
    Used:                         46.24GiB
    Free (estimated):             25.58GiB      (min: 25.58GiB)
    Data ratio:                       2.00
    Metadata ratio:                   2.00
    Global reserve:               70.91MiB      (used: 0.00B)

                            Data     Metadata  System              
Id Path                     RAID1    RAID1     RAID1    Unallocated
-- ------------------------ -------- --------- -------- -----------
 2 /dev/mapper/msata-debian 25.00GiB   2.00GiB 32.00MiB    22.97GiB
 1 /dev/mapper/sata-debian  25.00GiB   2.00GiB 32.00MiB    22.97GiB
-- ------------------------ -------- --------- -------- -----------
   Total                    25.00GiB   2.00GiB 32.00MiB    45.94GiB
   Used                     22.38GiB 754.66MiB 16.00KiB  


For RAID it in some place reports the raw size and sometimes the logical 
size. Especially in the "Total" line I find this a bit inconsistent. 
"RAID1" columns show logical size, "Unallocated" shows raw size.

Also "Used:" in the global section shows raw size and "Free 
(estimated):" shows logical size.

Thanks
-- 
Martin