Re: Have 15GB missing in btrfs filesystem.

[Marc MERLIN <marc@merlins.org>]

On Wed, Oct 24, 2018 at 01:07:25PM +0800, Qu Wenruo wrote:
> > saruman:/mnt/btrfs_pool1# btrfs balance start -musage=80 -v .
> > Dumping filters: flags 0x6, state 0x0, force is off
> >   METADATA (flags 0x2): balancing, usage=80
> >   SYSTEM (flags 0x2): balancing, usage=80
> > Done, had to relocate 5 out of 202 chunks
> > saruman:/mnt/btrfs_pool1# btrfs fi show .
> > Label: 'btrfs_pool1'  uuid: fda628bc-1ca4-49c5-91c2-4260fe967a23
> > 	Total devices 1 FS bytes used 188.24GiB
> > 	devid    1 size 228.67GiB used 203.54GiB path /dev/mapper/pool1
> > 
> > and it's back to 15GB :-/
> > 
> > How can I get 188.24 and 203.54 to converge further? Where is all that
> > space gone?
> 
> Your original chunks are already pretty compact.
> Thus really no need to do extra balance.
> 
> You may get some extra space by doing full system balance (no usage=
> filter), but that's really not worthy in my opinion.
> 
> Maybe you could try defrag to free some space wasted by CoW instead?
> (If you're not using many snapshots)

Thanks for the reply.

So right now, I have:
saruman:~# btrfs fi show /mnt/btrfs_pool1/
Label: 'btrfs_pool1'  uuid: fda628bc-1ca4-49c5-91c2-4260fe967a23
	Total devices 1 FS bytes used 188.25GiB
	devid    1 size 228.67GiB used 203.54GiB path /dev/mapper/pool1

saruman:~# btrfs fi df /mnt/btrfs_pool1/
Data, single: total=192.48GiB, used=184.87GiB
System, DUP: total=32.00MiB, used=48.00KiB
Metadata, DUP: total=5.50GiB, used=3.38GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

I've been using btrfs for a long time now but I've never had a
filesystem where I had 15GB apparently unusable (7%) after a balance.

I can't drop all the snapshots since at least two is used for btrfs
send/receive backups.
However, if I delete more snapshots, and do a full balance, you think
it'll free up more space?
I can try a defrag next, but since I have COW for snapshots, it's not
going to help much, correct?

Thanks,
Marc
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