Split-tail clustering with IBM xSeries servers?

[Martin Eskildsen <mae@tpack.net>]

Hello,

We have an IBM x345 xSeries server here and an EXP300 disk array
(running RAID5) that runs our central file server functions: Samba, CVS
respository, and NFS for other Linux servers.

That machine has grown in importance to us, and even though the hardware
has a lot of redundancy internally (dual this-and-that; can disable
failed CPU or RAM slot and reboot automatically) thus providing low
down-time, some parts are still single-points-of-failure, in particular
the motherboard and the RAID controller. If they die, we might be down
for a day or two until spare parts arrive. I don't trust service
contracts; IMHO they are usually a statement of intent, not a guarantee.

Thus, I'm thinking about setting up active-passive redundancy using a
second x345, the Heartbeat module from Linux-HA, and then share the
EXP300 disk array in a so-called split-tail configuration: One system
mounts read-write; the other system doesn't until the first system dies.

I'm considering such an expensive, complex measure on an internal server
simply because we would be in some pain if that server is down for a day
due to service. We, of course, have backups and all that, but it still
takes time bringing a replacement machine online if you need to restore
and configure it. We'd rather avoid that pain, if we reliably could.

Thus, I have two questions:

1. Has anybody tried setting up this kind of clustering using similar
hardware (IBM xSeries server and an external IBM EXP SCSI disk array)?
If yes, any experiences and hints you'd like to offer?

2. I would end up with two servers, both of which having dual power
supplies. In my setup, I run each "side" of the box on separate UPSes,
but those devices are "dumb" in the sense that they can't be controlled
directly (I can't programmatically turn on/off one outlet on the UPS
device). That's a problem, since I want to run STONITH (*) as part of my
Heartbeat setup, to avoid "split-brain" problems (both nodes mounting
the array read/write simultaneously). Any experience with power cycling
devices that can be controlled remotely, preferably via USB or RS232?

Thank you for your time,


/Martin Eskildsen
IT Administrator, Tpack A/S

(*) STONITH: "Shoot The Other Node In The Head". Yet another effect of
Open Source and volunteer efforts: Weird acronyms -- that name would
never have gotten through, say, the Microsoft Marketing Dept.   :-)
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