slowdown of zfs (tx->tx)

[Nicolas Rachinsky]

* Steven Hartland <killing at multiplay.co.uk> [2013-01-16 00:57 -0000]:
> 
> ----- Original Message ----- From: "Artem Belevich"
> <art at freebsd.org>
> To: "Nicolas Rachinsky" <fbsd-mas-0 at ml.turing-complete.org>
> Cc: "freebsd-fs" <freebsd-fs at freebsd.org>
> Sent: Wednesday, January 16, 2013 12:16 AM
> Subject: Re: slowdown of zfs (tx->tx)
> 
> 
> >It appears that lots of threads are stuck in
> >metaslab_activate->space_map_load_wait path. This sounds like CR#
> >6876962 in Solaris: "degraded write performance with threads held up
> >by space_map_load_wait(). This bug is fixed in patch 147440-05, -06 or
> >-07, which is current and contains the fix." Alas, I could not find
> >specifics on how the issue got fixed and whether the same fix is
> >present in illumos and FreeBSD.
> 
> That would tend to indicate its blocking on write. If this is the case
> yet the rsync is copying from this box, with little else doing writes
> it could be atime which is causing the issue.

I was probably misformulating my mail. The rsync writes to the local
zpool.

> A test for this would be to use the following to disable atime and see
> if that helps:
> zfs set atime=off [filesystem]
> 
> Also out of interest does the pool have many snapshots?

There are 115 filesystems. 84 of these have between 10 and 20
snapshots.

Nicolas
-- 
http://www.rachinsky.de/nicolas