[Samba] Question on how to get Samba to use larger pread/write calls.

[James Peach]

On 17 January 2011 08:14, Chris Duffy <cjd at small-tree.com> wrote:
> We are testing Samba 3 (and 4) on Fedora Core 13,
> 10Gbit connection with a Mac OS 10.6.4 system
> as the client.  We will be adding some Windows
> machines sooner or later with 10Gbit interfaces.
>
> We are seeing 100-150MBytes/sec read or write
> performance between the Mac and the FC13 system
> over 10Gbit interface but it should be capable of
> 400-500MBytes/sec.  We have a local raid
> on the FC13 system that runs 1GByte/sec locally
> using an Areca 1880-ix-16 raid card (6Gbit version).
> It has 16 fast Hitachi disks in a Raid5 format
> using xfs filesystem.
>
> The problem here is that samba is poking the Areca
> at 128KByte I/O's on preads and writes, i.e.
> shown to us using strace on the smbd daemons
> that are running.  Using vmstat/iostat/sar utilities,
> we see 100% utilization of the Areca card because the
> average wait time is real high and the average
> queue length to it is also high......too many
> small I/O's.....
> This is not the case if I run "fio" or "dd" locally
> to/from the Areca's raid using 1-4MByte I/O's.
> I see fast I/O...
>
> I do not see any way to increase the size of Samba's
> pread/write's in the smb.conf documentation.  I
> am sure it may be just a matter of getting the source
> code and making some changes to allow larger
> sized IO's but........and of course I suppose Windows
> clients may complain but....
>
> I remember that back in the old Irix days with the
> group of engineers in Australia I worked with,
> we had Samba screaming fast but not sure if they
> tweaked the version of Samba on Irix to do this.

Hi Chris :)

IIRC, we used a carefully tweaked read ahead module to make sure that
I/Os were hitting the disks properly aligned and of reasonable size.

http://www.samba.org/samba/docs/man/manpages-3/vfs_readahead.8.html

>
> Can you guys come up with a way for us to allow
> the reads/writes to/from the disks to be tunable
> up to say 4MB in size?
>
> Thx
> chris duffy
>
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-- 
James Peach | jorgar at gmail.com