file server question

David Collier-Brown davecb at
Mon May 14 13:22:52 GMT 2001

Lajber Zoltan wrote:

> We have been invited a tender by the Edu. ministry of Hungary. We
> are thinking about a "big" central file server for about 1500 named
> clients. We expecting about 400-500 simultaneous light office clients.
> The network is mostly fast ethernet, with gigabit backbone constructed
> with cisco elements (7206, 2948G-L3, 2924M-XL...).

	Ok, here's the assumptions and computation:

	500 office users * 1 IO/second * 8 KB/IO ~= 4000 KB/S
	2 * Ultra 200 CPU (the newest I have data for) = 5300 KB/S
	8 * 7200 rpm disks (ditto) = 4480 KB/S
	1 * fast Ethernet (tritto) = 6500 KB/S

	min(5300, 4480, 6500) = 4480 KB/S

	Therefor: if you configure less than 2 slow CPUs, 
	1 100 Mbit/S ethernet and 8 fast disks, you
	WILL fail.

	For each **active** user, allocate 1 MB of memory,
	as it will be used for disk cache for the disks
	you're serving (the application usage is much 
	smaller than that, more like ~760 KB)

	For each inactive user, allocate 1 MB of swap, so
	you won't refuse connections.

	You'll want to figure in 
		- room of estimation error (!)
		- headroom for expansion over time
		- upgradability
	The things to watch out for are
		- not having a box which is expandable to
		  the memory and cpus required for at least
	   	  twice the initia lestimate
		- buying too few disk **heads**, and not
		  RAIDing them together.  Throughput, not
		  capacity, is the problem of the 1990s.
		- starting with a single cpu: dual cpus
		  are A Real Good Thing for reducing 
		  latency and increasing response under


> Fortunately we are unix (sun+solaris, netfin+linux) shop, but have no
> experienc to size such machine.
> Our expectation is about an Ultra Enterprise 450, or a Fire 3800.
> Becouse the 5 VLANs, I prefering a quad fast ethernet NIC for load
> balancing, but a single gigabit interface possible, if it's better.
> Thanks for your effort.
> Bye,
> -=Lajbi=----------------------------------------------------------------
>  LAJBER Zoltan, Szent Istvan Egyetem, Godollo, IKKP-Informatika Osztaly

David Collier-Brown,           | Always do right. This will gratify 
Performance & Engineering Team | some people and astonish the rest.
Americas Customer Engineering  |                      -- Mark Twain
(905) 415-2849                 | davecb at

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