Re: What do the arguments of btrfs filesystem defragment do?

[Erik Logtenberg <erik@logtenberg.eu>]

Chris, thank you very much for your explanation. Indeed this clears
things up a bit.

>>> Caveat: Defragmenting a file which has a COW copy (either a snapshot
>>> copy or one made with bcp or cp --reflinks) will produce two unrelated
>>> files. If you defragment a subvolume that has a snapshot, you will
>>> roughly double the disk usage, as the snapshot files are no longer COW
>>> images of the originals.
>>
>> [2] https://btrfs.wiki.kernel.org/index.php/Problem_FAQ
>>
>> >From what I've heard on IRC this is still the case in current versions,
>> but the Btrfs(command) documentation contains no mention of this.
> 
> This is still true.

Is there a decent way to have btrfs compress already existing files
(that were written before compression was enabled) without hurting any
of the internal structures such as snapshots?
The goal is to increase free disk space and possibly performance, not to
expload disk usage by breaking COW relations. So given your reply, I
assume that defragmenting all files is not the right way (?)

Kind regards,

Erik.