Samba Load Testing at Brunel University

[Peter Polkinghorne]

BACKGROUND:

We wanted to find out how many PC clients our typical Sun server could
support using Samba.

In the past we have had a figure of 30 class room or 100 office clients
using PC-NFS, being supported by a Sparc 2 in a shared ethernet environment.
However we now have switched fast ethernet, Windows NT 4.0 clients and Sun
Ultra servers using Samba.  So how many clients will a server support in our
new environment?  The support here means supplying PC applications,
home directories are a separate service with different sizing requirements.

SET UP:

System: Cedar - Ultra 5/270 with 192Mb of memory and 4 & 8 Gb SCSI disks
	and Fast Ethernet (full duplex).

Software: Solaris 2.5.1 and Samba 1.9.18p10

Role: All NT applications software supplied to NT 4.0 sp3 workstations.

TEST:

This machine already serves around 200 NT clients - admin users.

We have around 450 NT clients on the campus - by map changes (NIS for those
interested - we use NISgina), we moved them all in 3 stages to Cedar from the
other 9 servers and observed the loading.  The extra clients comprised of
around 80 class room PCs and 170 or so office machines used by staff and
post grads.  The office machines are characterised by long login sessions
and more diverse applications, whereas the classroom machines have short
term use and tend to stick to word processing and web browsing.

I tested the responsiveness by using a NT client and measured time to
login and time to load Word 97.  This enabled us to check whether the user
perceived performance was acceptable.

RESULTS:

User:

To the user point of view - service did not degrade by and large.
My measured login and Word 97 startup times did not change.
One or two users had difficulty connecting - possibly due to the resource
intensive nature of the logins - each smbd took 7 secs CPU just to service
the login - this is something we are investigating from the client side.

System:

I used Samba Snap - see ftp://ftp.brunel.ac.uk/cc/peter/samba/
a little perl utility that condenses smbstatus output to observe usage:

        Connections Shares  Files  %shared memory (400k)
Normal:  120         300    2,500   33%
Peak:    344         600    6,300   69%

The load on cedar did increase - the memory was not really adequate for the
number of Samba processes - Swap space had to be raised to 460Mb.
SAR indicated that the idle time went down to less than 20% for busy periods
at peak test as opposed to 60% for normal load.

The disks did not from SAR appear to be too heavily loaded, apart from for
swapping.

Network traffic at normal load is 300 k bytes a second (2.4 Mbps),
whereas at peak it was 1000 k bytes a second (8 Mbps).

CONCLUSION:

Overall we were pleased that such a relatively lowly server could hand out
PC applications to as many clients as well as that.

We plan to use Sun Ultras for supporting upto 60 classroom and 400 office NT
workstations per server and ensure there is a reasonable mix of office and
classroom machines.

OTHER THOUGHTS:

Using Samba 2.0.X should improve performance (or so I have been lead to
believe).

With Solaris 7 (and other OSs) the noatime type mount options would help.

More memory would have helped cedar or may be we were hitting other barriers?

Client behaviour is important.

Can dig up more figures if useful ...

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| Peter Polkinghorne, Computer Centre, Brunel University, Uxbridge, UB8 3PH,|
| Peter.Polkinghorne at brunel.ac.uk   +44 1895 274000 x2561       UK          |
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