Re: 97% full system, dusage didn't help, musage strange

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

在 2024/12/15 06:43, Leszek Dubiel 写道:
>>
>>
>> btrfs filesystem usage -T
>>
>
> Overall:
>      Device size:          16.28TiB
>      Device allocated:          16.24TiB
>      Device unallocated:          38.02GiB
>      Device missing:             0.00B
>      Device slack:             0.00B
>      Used:              15.75TiB
>      Free (estimated):         264.00GiB    (min: 264.00GiB)
>      Free (statfs, df):         257.98GiB
>      Data ratio:                  2.00
>      Metadata ratio:              2.00
>      Global reserve:         512.00MiB    (used: 160.00KiB)
>      Multiple profiles:                no
>
>               Data    Metadata System
> Id Path      RAID1   RAID1    RAID1    Unallocated Total    Slack
> -- --------- ------- -------- -------- ----------- -------- -----
>   1 /dev/sdb2 5.39TiB 28.00GiB 32.00MiB    13.00GiB  5.43TiB     -
>   2 /dev/sdc2 5.39TiB 20.00GiB        -    13.03GiB  5.43TiB     -
>   3 /dev/sda3 5.38TiB 34.00GiB 32.00MiB    12.00GiB  5.43TiB     -
> -- --------- ------- -------- -------- ----------- -------- -----
>     Total     8.08TiB 41.00GiB 32.00MiB    38.02GiB 16.28TiB 0.00B
>     Used      7.84TiB 37.67GiB  1.47MiB
>
>
>
>>>
>>> But unallocated space didn't increase.
>>>
>>>
>>
>> Why did you expect it to increase? To free space balance need to pack
>> more extents into less chunks. In your case chunks are near to full
>> and extents are relatively large, so chunks simply may not have enough
>> free space to accommodate more extents. You just move extents around.
>>
>
> Ok. I didn't exactly know what chunks are compared to extents.
>
>
>
>
>
>> Relocating one chunk simply moves extents from this chunk to another
>> location. It does not free any chunk. You can only get more
>> unallocated space when you are able to pack extents from two (or more)
>> chunks into one chunk. Which is only possible if chunks are filled to
>> 50%.
>>
>
> Thank you for explanation.
>
>
>
>
>>> What should i do next?
>>
>> It looks like your filesystem is simply full. Do you have reasons to
>> believe that it is not true?
>
>
> It is backup server. It should be almost full.
> I have a procedure that:
>
> — removes old snapshots if free space is less then 250 GB
> — starts balancing if there is less then 8GB of unallocated space on any
> disk
>
>
> It failed now — there is 258 GB free, but balancing didn't help to
> restore unallocated space.

Because there isn't that much free space to reclaim in the first place.

Your data and metadata chunks are already very highly utilized, you can
increase the dusage/musage and retry, but they will only bring marginal
gain if any.

The only way to go next is start deleting more
snapshots/subvolumes/files/etc.

With more data/metadata space released, then try musage/dusage again
which can free up some space.

Thanks,
Qu