[Samba] Samba process throttled back?

Lang, Rich
Fri, 17 Jun 2011 13:39:16 -0000

Hello,

We are running Samba 3.0.33 on a 2-node Linux cluster running RedHat 5.6 ES.
Its primary application is to serve out a single network drive to support our
business (out 350GB in size).  For several years, this solution has been running
flawlessly.  File access was almost as fast as a local disk, so putting files on
the server was never a problem.  Our clients are running mostly Windows XP Pro.
We have a few Windows 7 clients.

Almost a year ago, that changed.  Applications written in VB 6.0 that read files
from the server started showing *significant* performance problems.  What used
to take seconds now takes more than a minute to finish.  Moving the file to a
local disk brought the speed back up to where it should be.  Moving the file to
a Windows 2003 or 2008 server also provided good throughput.  All clients
experience this same problem.

I ran "strace -f" against the smbd process that is assigned to my
desktop and then ran the VB application to see what the daemon was up to.  I
discovered that it went through a process of opening the file several times and
reading data from it, using progressively smaller buffer sizes until is settled
on using a buffer size of 1, which it used for the remainder of the file I/O
session.

I've attached the smb.conf file for your reading pleasure.  I can attach the
strace output file if that would be helpful.

I suspect that something changed on the Windows desktop side to bring this
about, since we made no changes to our VB code at all.