[Samba] aio settings for samba 4.3

Volker Lendecke vl at samba.org
Wed Jul 20 08:58:38 UTC 2016


On Tue, Jul 19, 2016 at 12:42:53PM -0700, Jeremy Allison wrote:
> On Tue, Jul 19, 2016 at 12:49:09PM -0500, Russell R Poyner wrote:
> > I'm tuning a samba 4.3 install on freebsd and I'm confused about aio
> > settings.
> > 
> > I've loaded the freebsd aio kernel module and tried various values
> > or aio read size and aio write size, but it seems to make no
> > difference in the speed.
> > 
> > Using MS diskspd against a samba share from a fast zfs pool I get
> > something like 25MB/s tops. That's well below the capacity of my Gb
> > network and my disk system. FWIW iperf shows >900Mbits/sec in both
> > directions on the link.
> > 
> > # smbd -b|grep aio
> >    vfs_aio_fork_init
> >    vfs_aio_posix_init
> >    vfs_aio_pthread_init
> 
> You don't need these, modern Samba includes a pthread pool
> implementation that will parallelize SMB io requests.

The main reason for our user-space threaded approach is lack of aio in
Linux. Proper kernel support for posix AIO might be faster than our
implementation. "vfs objects = aio_posix" will give you that.

This needs very thorough performance testing. If it turns out to be
faster than our threaded aio on FreeBSD, we might have to revive
the aio_posix module, it went away last year.

Volker



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