Re: btrfs thinks fs is full, though 11GB should be still free

Remi Gauvin
2023-12-13T01:49:49Z

On 2023-12-11 10:27 p.m., Christoph Anton Mitterer wrote:
>
> Well the manpage warns from using on large DB workloads... I mean
> Prometheus is not exactly like a DB, and I would have naively assumed
> that at least the chunks were written not as many small random
> writes... but apparently they are.
>
> Also, this a VM, so the storage volume is actually something Ceph
> backed, which the university's super computing centre provides us with.
>
> I wonder if I do autodefrag on all that, if it doesn't just kill of our
> performance even more?

On SSD, I like to use compress-forced option and a daily defrag with
target size 128k to eliminate space wasted by fragmentation.
(Compressed extents are max size 128KB)

However, compression will destroy sequential file read speed on spinning
disks, (presumably due to the small extent size, possibly not landing on
disk in order, I'm not really sure why read speed is badly affected when
write speed is not.)

If there are no snapshots or reflink copies, you can use defrag with
target size 128MB (at whatever frequency you need.) to eliminate wasted
space.