[Samba] 1 BDC per 50 Clients? Can that really be true? (HOWTO)

D Canfield canfield at uindy.edu
Thu Jan 27 17:16:55 GMT 2005

In "the 500 user office" section of the Samba Guide,  John Terpstra 
lists some seriously disappointing numbers for Samba scalability.  To 
quote, "As a general rule, there should be at least one Backup Domain 
Controller per 50 Windows network clients. The principle behind this 
recommendation is the fact that correct operation of MS Windows clients 
requires rapid network response to all SMB/CIFS requests. The same rule 
says that if there are more than 50 clients per Domain Controller they 
are too busy to service requests."

Our lab manager has read this document, and believes that we need to add 
19 more servers to a domain that is currently served by one box in order 
to "do things right." It seems to me that this quote must simply must be 
a typo, or that it's somehow horribly out of context (the example is 
discussing a multi-office configuration with a 15Mb uplink afterall), as 
it is completely inconsistent with what I've seen myself or read 

We currently have 400 lab machines as domain members, plus another 500 
or so non-domain windows clients (used by office personnel) with up to 
250 of those total clients using the server simultaneously (we use it 
mostly for file sharing and domain logins, very rarely do we run 
applications from the shares).  At this point, our samba server sits 
idle for the most part when serving all of those machines.. no memory, 
disk, or CPU bottlenecks that I can see.  We would like to add those 
remaining 500 clients to the domain (mainly just because we can't find a 
way for non-domain machines to edit ACL's on shares), and while I agree 
that it's time for us to add a BDC for good measure, disagreement over 
the scalability has become a sticking point.

I've read on this list people discussing thousands of domain members 
with hundreds of simultaneous users, and nowhere else have I seen 
anything even close to this 50-users per BDC number.  And if you think 
about it, if these machines are going to be too busy handling domain 
communication traffic, wouldn't that mean that 20 servers/1000 clients 
would practically saturate a typical  network just sitting idle? Can 
someone shed some light on this for me?



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