Extreme performance falling on ZFS by durable operation of a server

[Alexandr D. Sergeev]

On Thu, Apr 08, 2010 at 01:14:42PM -0700, K. Macy wrote:
> Hi Alexandr,

Hi Kip,

> 
> - How much memory do you have?

4Gb.
Applications consume a lot of memory, is partially used swap (~1Gb, but without active i/o).

We have planned increase in memory to 16G

> 
> - What are your ARC settings?

Settings is default, that recommended for amd64 kernel.
But I am not assured that it is optimal.
Thus sysctl variables are automatically sets to:
vfs.zfs.arc_max ~800Mb
vfs.zfs.arc_mim ~128Mb

Now the next reboot was required.
Together with which following settings have been made:

vm.kmem_size=2048M
vfs.zfs.arc_max=1536M
vfs.zfs.arc_min=1024M
vfs.zfs.vdev.cache.size=64M

Let's look, as it will affect.

However there is confidence that no problem at a size of ARC.
Even at 200Mb ARC, productivity should not fall so strongly.

> 
> Thanks,
> Kip
> 
> On Thu, Apr 8, 2010 at 8:32 AM, Alexandr D. Sergeev <ales at ripn.net> wrote:
> > Hi, all!
> >
> > There are problems with a server on FreeBSD 7.2 CURRENT (6 Jul 2009), carrying out the task of mail server SMTP, IMAP.
> >
> > Messages are stored in maildirs on file system ZFS (mirror of 2 SAS 3k drives).
> > Dovecot is used as IMAP server.
> >
> > After reboot the system works perfectly, however, somewhere in a month, at the same load, arise periodic long delays at opening of new letters.
> >
> > Judging by output iostat -x -w 1, during these moments the disk subsystem is strongly loaded.
> > %busy disks comes nearer to 100 %. Readings nearby 300 per sec prevail. and approx. 10MBytes per sec.
> >
> > Somebody can advise, what diagnostics needed, for understanding of the reason of problems?
> >
> > There is an opinion that a problem with ZFS.
> >
> > Probably, it does not have enough memory. Because during the periods of occurrence of a problem,  ARC is have less 300MB:
> >
> > vmstat -m
> > ...
> >      solaris 1245732 274745K       - 25872717949  16,32,64,128,256,512,1024,2048,4096
> > ...
> >
> > Or it is bug of ZFS implementation.
> >
> > --
> > Best regards,
> > Alexandr D.Sergeev
> > _______________________________________________
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> > http://lists.freebsd.org/mailman/listinfo/freebsd-performance
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> >

--
Best regards,
Alexandr D.Sergeev