Re: Poor performance of btrfs. Suspected unidentified btrfs housekeeping process which writes a lot

[Gabriel <g2p.code@gmail.com>]

Hi,

> After mounting the system with noatime the problem disappeared, like in 
> magic.

Incidentally, the current version of bedup uses a private mountpoint with 
noatime whenever you don't give it the path to a mounted volume.  You can 
use it with no arguments or designate a filesystem by its uuid or /dev 
path.

> All the writes must have came from the dealyed metadata copy process. 
> Once all the metadata copy-update was done, file system speed was back 
> to normal, but once the new day broke out, all the copying business 
> needed to done again... This in 100% describes all the odd behavior.
> 
> In particular apparently the problem had nothing to do with my complex 
> block device setup, nor with bedup, nor with unison.
> 
> Thank you again, Andrew!
> 
> P.S. Maybe it is not be decided by me, but this small message about 
> performance (not even labeled as warning) in 
> https://btrfs.wiki.kernel.org/index.php/Mount_options IMHO should have 
> been made more conspicuous, maybe put somewhere when the snapshot 
> mechanism is described or in FAQ. I'll try to fix it.