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so I reply using mail-archive)
> Try btrfs-show-super <device>. The incompat_flags section enumerates the
> flags that are on (at least with a reasonably new btrfs-progs).
Thanks a lot for this hint - I totally missed that, since I only looked
at manpages and features of the "all-in-one" btrfs tool up to now.
Also thanks for the hint to /sys/fs/btrfs, this is even more readable!
And thanks a lot for your detailed answer(s) in general!
> In general it should be safe to activate flags via btrfstune, but since
> they'll generally apply only to newly written data, any benefits on a
> mature filesystem will be limited. For that reason as well as to get the
> benefit of 16K nodesize which you can't except at creation, I recommend
> backing up and recreating the filesystem from a fresh mkfs.btrfs.
That would certainly be the best option, however,
I have two issues with that:
- Any replay of a backup will do a lot of writes on the SSD,
reducing lifetime.
- I did not yet figure out a working way to get a "complete" backup for a
btrfs.
btrfs send is too slow for me, and rsync does an incomplete backup,
since all FS-special attrs (like the NOCOW attr from 'chattr +C')
are not copied, even when xattr copy is on.
My last backup replay was from an rsync backup (these I do regularly)
and afterwards I did a manual fixing of these special attrs, which is some bit
of extra work.
Also, the machine is offline during backup replay,
while I could still use it during a simple rebalance.
The good news is my old FS already has 16K leafsize, it's only missing skinny
metadata
(and no-holes, apparently that's not default in mkfs.btrfs yet?).
This reduces the scope of my question a bit - is it sufficient and worthwhile
to "btrfstune -x"
and then "btrfs balance start -musage=0 /" to convert all metadata, and thus
gain some space?
Or are the gains not worth it and I should just wait until the next time I need
to replay a backup for other reasons?
Cheers and thanks for your reply,
Oliver
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