freebsd stable - Feb 2012 - Swap on zvol - recommendable?

Hi, all,

is it possible to make a definite statement about swap on zvols?

I found some older discussions about a resource starvation
scenario when ZFS arc would be the cause of the system
running out of memory, trying to swap, yet the ZFS would
not be accessible until some memory was freed - leading to
a deadlock.

Is this still the case with RELENG_8? The various Root on
ZFS guides mention both choices (decicated or gmirror
partition vs. zvol), yet don't say anything about the respective
merits or risks. I am aware of the fact that I cannot dump to
a raidz2 zvol ...

Thanks for any hints,
Patrick
-- 
punkt.de GmbH * Kaiserallee 13a * 76133 Karlsruhe
Tel. 0721 9109 0 * Fax 0721 9109 100
info@punkt.de       http://www.punkt.de
Gf: J?rgen Egeling      AG Mannheim 108285

I can just tell you I had this problem still in 8.1 and it was a HUGE problem. 
System stalled every two weeks or so. Now when the swap is moved away from
zfs it works fine.


On Feb 6, 2012, at 11:57 AM, Patrick M. Hausen wrote:
> Hi, all,
> 
> is it possible to make a definite statement about swap on zvols?
> 
> I found some older discussions about a resource starvation
> scenario when ZFS arc would be the cause of the system
> running out of memory, trying to swap, yet the ZFS would
> not be accessible until some memory was freed - leading to
> a deadlock.
> 
> Is this still the case with RELENG_8? The various Root on
> ZFS guides mention both choices (decicated or gmirror
> partition vs. zvol), yet don't say anything about the respective
> merits or risks. I am aware of the fact that I cannot dump to
> a raidz2 zvol ...
> 
> Thanks for any hints,
> Patrick
> -- 
> punkt.de GmbH * Kaiserallee 13a * 76133 Karlsruhe
> Tel. 0721 9109 0 * Fax 0721 9109 100
> info@punkt.de       http://www.punkt.de
> Gf: J?rgen Egeling      AG Mannheim 108285
> 
> 
> 
> _______________________________________________
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>

On Mon, Feb 13, 2012 at 9:02 AM, George Kontostanos
<gkontos.mail@gmail.com>wrote:
> >
> > I can confirm that this is still a problem on 8.2 and 9.0.
> >
>
>
> You can not compare 8.2 with 9.0 per ZFS. What problems are you facing
> with your swap in 9.0 ?
>
I suppose you are having problems similar to the following:

http://lists.freebsd.org/pipermail/freebsd-fs/2012-January/013546.html

Perhaps setting vfs.zfs.arc_max to some reasonable value might help, but
that is just a guess.

-- 
Adam Vande More