Re: [sheflug] Assessing server requirements

[Gary Stimson <bulk [at] xxxxxxxxxxxxxx>]

David Willington wrote:
> Thanks for the pointers. I was vague because I've only a rough idea of
> how many machines the school has and how much use is likely to be made
> of the server. However your guestimate looks good and 'you don't need a
> particularly powerful server' is good news. For disk usage, I was
> planning to allocate 50Mb a user. How much spare capacity would you
> recommend I leave on a hard drive so that it performs as it should?
> 
> Do I need to think about hardware differently from the way I'm used to?
> At the moment I just buy the cheapest bits I can find for running at
> home, and use managed hosting for websites so I've not had to deal hands
> on with a server as such. Are the components for a server the same sort
> of things as for a desktop?

Rather than "cheapest", go for "best value". Some things included in
"value":
- amount of time needed to set up and maintain.
- life expectancy. This includes both reliability (how long will it last
before breaking) and capacity to handle growth (how many years will it
last before needing a replacement)

40GB hard disks are the cheapest at £25 but 160GB are about £39, 250GB
£47 and 300GB £57.

Forgetting that 80% of users will probably use less than 20% of their
allocated space, the maxiumum space you want is 1600 users x 50MB = 80GB.

If this server is just being used for moodle then 2 x 160GB in a RAID 1
(=about 145GB usable space) mirror will do nicely. If it's likely to be
used for more applications and as a general filestore then I'd probably
go with 3 x 250GB in RAID 5 (=about 460GB usable space). Seagate and
Western Digital drives have good reliability and 5 year warranties.
Maxtors are about £2 cheaper but have a higher failure rate so avoid.

1GB RAM will be fine.

A single Pentium 4 3.0GHz is good value and more than ample for the
processor needs.

You don't need powerful graphics - on-board graphics from your
motherboard will be fine. Get a motherboard that doesn't have any little
fans on it because they develop an irritating whine in a year or two,
then stop working and take the whole board with them. Check that linux
has good support for the motherboard's chipset before buying.

If you're building yourself then get a good case with good quality
branded power supply. Decent power supplies cost perhaps £50 but cheap
ones are a false economy because they tend to develop noisy fans then
blow after a short time. A 260W PSU would be ample - the max power draw
of this spec is about 130W.

If a server with the same processing power but a lower power consumption
would be attractive, go see Peter at Very-PC on Infirmary Rd. He's
assembled PCs using the AMD Turion 64-bit mobile processor. This spec:
AMD Turion
1GB RAM
2 x 160GB 3.5" Seagate or WD HDD
Midi case with quality branded quiet power supply.
That spec would draw about 60W and save about £45 of electricity per
year if left on 24/7.

> Will mug up on RAID

Software RAID will be fine. Just make sure that you set it to send you
an email if it has a problem and test that outgoing email works OK. I
think this is the HowTo:
http://www.tldp.org/HOWTO/html_single/Software-RAID-HOWTO/

>>After disks, the next biggest causes of server failure are failed fans
>>and PSUs. If you are supporting the hardware, consider using lm_sensors
>>to monitor fan speeds and CPU/case temperatures and alert you where
>>necessary. Therefore check the motherboard is lm_sensors compatible.

The easier alternative to this is to make sure the BIOS is set to shut
the PC down on overheat. As the school has technicians, they'd hopefully
notice the whining grating noise of a failing fan and change it.

> Backups are already in place - I think there was some surprise that
> Linux could back up onto a windows server!

I've never done it that way around! Do file ownerships and permissions
get preserved OK? Or are you using a tar archive to make sure they do
get preserved?

Gary

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