[Samba] performance problem with 3.2.8: unbuffered reads for some users

Alexander 'Leo' Bergolth leo at strike.wu-wien.ac.at
Wed Mar 4 12:56:26 GMT 2009


I'm experiencing strange performance problems after upgrading to samba
3.2.8 from 3.0.30.

For all users except smbadmin (who has administrative rights), read
performance is _very_ bad. Looking at the read-requests using filemon
and wireshark, I found out that for those users, every read is handled
transparently (unbuffered) over the net. (I.e. a 2 byte read-request of
the application leads to a 2 byte Read And X Request over the net.)

If the user is smbadmin, reads are block buffered. (A 2 byte
read-request of the same application as above leads to a 4096 byte Read
And X Request over the net.)

Clients are WinXP SP3.
For details, see my test below..

When are those buffering parameters negotiated? Do you have any idea why
the behavior depends on the connected user?
Any hints how I could further track down this problem?


The test was done using 2 byte reads on the windows box:
perl -le 'sysopen(F, "R:/firefox/LICENSE", O_RDONLY);
  do { $n= sysread(F, $buf, 2) } while ($n)'

The result can be found here:
smbadmin (buffered reads):

abergolth (unbuffered reads, same box):


e-mail   ::: Leo.Bergolth (at) wu-wien.ac.at
fax      ::: +43-1-31336-906050
location ::: IT-Services | Vienna University of Economics | Austria

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