[HCoop-Discuss] hardware advice

[Adam Megacz]

Adam Chlipala <adamc at hcoop.net> writes:
>> No; I'm saying that RAID and hot-swap bays make disks the only place
>> where it's sensible to buy cheap-and-unreliable parts.

> But, implicit in that, are you saying that the mean time to failure for 
> other parts is low enough, when we buy "reliable" versions within our 
> price range, that it's OK to only be able to replace parts at the speed 
> of shipping them across the country? 

Ideally you should have enough machines (two is probably enough) in
every physical location so that if one of them experiences a hardware
failure you can call up the colo monkeys and have them move the drives
from the dead machine to the working one.

You should buy reliable hardware so that this doesn't happen very
often.  When it does, the result will be several hours of downtime but
(unless somebody drops the ball) less than a day.  And the downtime
would only be experienced by those users whose data resided on the
failed machine.

I don't know if hcoop can afford this, but ideally you would want at
least four AFS servers: two physical locations each having two
servers.  Based on the prices I pay for gentzen, that would be $2000
to buy the hardware and $220/month.

Login servers (ie everything except databases, AFS, and Kerberos)
should be disjoint from these four machines.  There should be at least
two login servers, and we should make sure members know that we do not
guarantee the uptime of any particular login server -- just that at
least one will be up at any given time.  Members should ensure that
they do not rely on the upness of any particular login server.

> Use Xen virtualization on both machines, so that we can create many 
> virtual servers and move them among machines as needed.

Regarding v12n, I won't say I'm against it, but I think it creates a
good bit of hassle that I'd rather not deal with.  The way I think of
it, domtool is a v12n technology that works at the application layer
(for each application domtool knows about).  I'm not sure that
Xen/OpenVZ/whatever really adds much once you've got domtool.

  - a