> We need to assemble and put into service a couple of large machines
> to act as a web cache (using the squid software).

Before going any further, you may wish to consider the solutions offered
by NetApp (http://www.netapp.com), as well as the Vixie Enterprises Web
Gateway Interceptor, available from Mirror Image 
(http://www.mirror-image.com).

Bear in mind that I'm wearing a FreeBSD hat.

> The choice is either SUN systems running slowaris or large PC's
> running either NetBSD or FreeBSD. The management are inclined to the
> former, but may be willing to entertain the latter if I can convince
> them it will work, hence need I need a bit of feedback from people
> who run PC's with large amounts of memory and SCSI disk.
> 
> My first stab at a system would use a Pentium II board with 512Mb
> Memory and a 333Mhz processor. The system would boot from the on-board
> EIDE controller via a 2Gb system disk. The cache area would be two
> strings of 4 fast wide 9Gb SCSI II disks plugged into an Adaptek 3940 
> ultra controller. We would probably use an Intel Express 10/100 Ethernet
> adaptor (or two) as the network connection.

There are a number of poor design decision here.

 - The PII is not suitable for large server systems, as it will only 
   cache the first 512MB of memory.
 - The 3940 is a poor choice as a cache controller; you would be better 
   off with either a DPT RAID controller card, or an external SCSI:SCSI
   RAID (eg. a CMD unit).  The latter is generally a better idea.
 - Booting (and thus putting your root filesystem and probably swap) on 
   an IDE disk creates an unnecessary bottleneck.  Use another SCSI 
   disk, preferably on its own controller.

> 2) Will 512Mb of memory break anything ? (I know I will have to tell the
>    kernel the true memory size)

It is the usable limit for the PII processor.  For your application, a 
P6/200 may be better.  It's dubious as to whether you will be able to 
saturate such a processor unless you try *really* hard.  FreeBSD is 
pretty good about automating memory detection (and is getting better).

> 3) Has anyone any experience of a machine with this sort of configuration ?

Yes.  More verbosely, FreeBSD systems are frequently used in similar,
and larger, configurations.  For example, ftp.cdrom.com is a P6/200 with
1GB of memory and 224GB of disk.  It's currently averaging an output of
about 44Mb/s on a 24-hour basis.  Various other examples have already 
been given; suffice to say that you're not going to be taxing it much. 
8)

> 4) Has anyone used any of the Supermicro boards e.g. P6DBS with the builtin
>    Adaptec Dual Channel UWSCSI ? or got suggestions for other suitable
>    motherboards (preferably ones with will take up to 1Gb RAM) I should 
>    point out that 'the management' would REALLY like to use a commercially
>    available box rather than me build one out of bits !

It is pointless putting more than 512MB of memory in a PII board, as 
previously mentioned.  If you're really serious about a monster system, 
you would be able to get FreeBSD up on the Axil Northbridge NX-801 
(http://www.axil.com/) with a little help from one of the folks at Axil.
Other large server systems worth considering (and less expensive) are 
the Compaq Proliant and IBM NetFinity systems.  Some basic rules:

 - If you want more than 512MB of memory, you need to use Pentium Pro 
   processors.  (This may change with new PII models; I'm a few months 
   out of date.  Be very certain to check this carefully.)

 - If you want more than one processor, you will want to go with 
   one of the FreeBSD-current snapshots.  For 2- and 4- processor 
   systems, there are plenty of testimonials indicating success.  
   Beyond this you may require some assistance, depending on your 
   hardware.


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\\  Sometimes you're ahead,       \\  Mike Smith
\\  sometimes you're behind.      \\  mike@smith.net.au
\\  The race is long, and in the  \\  msmith@freebsd.org
\\  end it's only with yourself.  \\  msmith@cdrom.com