Re: btrfs differential receive has become excrutiatingly slow on one machine

[Marc MERLIN <marc@merlins.org>]

On Sun, Sep 14, 2014 at 05:18:36PM -0700, Marc MERLIN wrote:
> On Mon, Sep 08, 2014 at 10:49:01PM +0100, Filipe David Manana wrote:
> > Hi Marc,
> > 
> > Does the sum of all reads from the stream file (fd 3) gets anywhere
> > close to the total btrfs receive time? (or even more than 50%)
> > Can you paste somewhere the full output of strace (with -T option)?
> 
> Sorry for the lack of answer, I lost the snapshot I used for that mail,
> so it was not possible to do again easily.
> Because my backups were so hopelessly behind, I did a full resync of
> /var, i.e. not a differential send (300GB or so). The copy went at about
> 25GB/h, which wasn't bad at all since was over wifi (took about 14H).

Sigh, now that I'm resyncing my laptop I just rebuilt after the btrfs
crash, to my server (both running 3.19.5+), full btrfs sends (i.e. not
incremental), are taking ages.

I'm seeing less than 100GB/day on my home network when my tcp
connections over wifi easily get 50MB/s

Right now I'm seeing the equivalent of aout 1MB/s, or 50 times less than
what my network connection can do.

Last time I tried to strace btrfs send, it killed the process with
SIGPIPE and I lost a full day of sync and had to start over :(

It's a broad question, but how can I diagnose btrfs send being so slow
without taking the risk of killing my connection?
(if there is no good answer on this one, I can try another sync later
with -vvv and strace if you'd like)

Thanks,
Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/                         | PGP 1024R/763BE901