Re: ENOSPC errors during raid1 rebalance

[Michael Russo <mike@papersolve.com>]

Chris Murphy <lists <at> colorremedies.com> writes:

> You could also try a full defragment by specifying -r on the mount point
> with a small -t value to effectively cause everything to be subject
> to defragmenting. If this still doesn't permit soft rebalance, then maybe
> filefrag can find files that have more than 1 extent and just copy 
> them (make duplicates, delete the original). Any copy will be
> allocated into chunks with the new profile.

I would think so too.  But it doesn't seem to be happening. 
Here is an example with one file:

root@ossy:/mymedia# filefrag output.wav
output.wav: 2 extents found
root@ossy:/mymedia# /usr/src/btrfs-progs/btrfs fi de -t 1 /mymedia/output.wav 
root@ossy:/mymedia# filefrag output.wav
output.wav: 2 extents found

btrfs does not defrag the file. And copying the file usually
doesn't defrag it either:

root@ossy:/mymedia# cp output.wav output.wav.bak
root@ossy:/mymedia# filefrag output.wav.bak
output.wav.bak: 2 extents found

I even tried copying a large file to another filesystem (/dev/shm),
 removing the original, and copying it back, and more often than not 
it still had more than 1 extent. 

If I copy each file out to another filesystem and then back, will btrfs 
not use any of the space on the "single" and just re-allocate space 
on the RAID1 like I want it to?