Forum OpenACS Q&A: little question about a server

Posted by David Kuczek on 05/05/01 11:16 PM

I want to get a DELL 2550 rack optimized, but I am not sure what to do
about the raid.

I would like to start with a single 36gb harddrive and a single 1Ghz
CPU, because this would be the cheapest version for the beginning...

If I switched to a raid system in the future, I would have to
recompile the kernel or build a new one... is this correct?

How much downtime does this usually mean?

Can you build the kernel anticipating what kind of hardware you will
put in? And then after you put in all the hardware restart the server
with the already built new kernel?

What is the common procedure with this or should you get a raid from
the very beginning?

Thanks

2: Response to little question about a server (response to 1)

Posted by Malachi Kenney on 05/06/01 10:30 AM

Finagle's Law applies in full force here. In my experience, switching to RAID later usually means switching to a different, RAID capable system rather than upgrading a live system to RAID. The former method (a standby system) is both faster and safer than trying to upgrade a single production box.

The procedure for upgrading the live system will mean full backups to different media and a complete restore after the upgrade. You can, thanks to Finagle's Law, count on the downtime between those two operations being measured in hours rather than minutes unless you have practiced the drill with that specific hardware in advance.

An important factor here is that the kernel configuration bears very little relation to this operation. You can indeed configure the kernel beforehand. You can not, however, entirely configure the hardware RAID and the filesystems (especially if you plan to use the single drive in the final RAID configuration). As an example, adding drives in to the machine and then initializing a 3 drive harware RAID 5 with the standard Dell Perc tools may take 40 minutes of complete downtime before any actual migration takes place.

If you know you need hardware RAID then it is simpler to go with that configuration from the get go. Otherwise, unless you really know what you're doing, you should plan on non-trivial downtime.

3: Response to little question about a server (response to 1)

Posted by Mike Sisk on 05/06/01 04:34 PM

I don't know for sure about the 2550 but this is how it works on
our Dell 2450s with RedHat 6.2:

The 2450s have the hardware RAID built into the motherboard. If
you order a system without RAID it's not enabled. If you later
decide to upgrade you get a hardware key that fits into a socket
on the motherboard and a 64-MB cache memory SIMM.

When we first got these systems about a year ago they were
supplied with a compiled kernel with a closed-source driver for
the RAID. Later Dell updated the kernel and open-sourced the
RAID driver as a kernel module.

We ordered all our systems with RAID so I don't know exactly
what kernel configuration you'd get if you don't order it.

On systems that are dual-CPU capable you get a kernel built
with SMP--even if you only order a single-cpu system.

I'd get the RAID to start with as Dell's pricing on upgrades is
pricy.

4: Response to little question about a server (response to 1)

Posted by David Kuczek on 05/08/01 12:04 PM

Hello Mike,

did you buy your server with that hyper-cheap 😉 Dell-Ram from the very beginning or did you get it with the standard 2x64mb and then got addititonal Ram at i.e. Crucial and rebuilt the kernel?

Did you reinstall RH 6.2 on your 2450 or did you go with Dell's configuration and didn't touch anything afterwards?

Is there anything tricky about installing RH 6.2 on a 2450? Does Dell have a guide for installing RH on their servers?

Thanks

5: Response to little question about a server (response to 1)

Posted by Mike Sisk on 05/08/01 03:12 PM

When we ordered the systems I specified them to have
2x256-MB chips. I don't recall the brand of memory but they're
standard 133MHz ECC chips. Several of these machines have
uptimes approaching 300 days so I assume the quality of the
memory has been adequate. ;>

I recompiled the kernel on all these machines since they came
to us with the stock Red Hat 6.2 kernel which has several
problems. Dell now has RPMs available for updated kernels.
Dell ships these with the full Red Hat install so expect to spend
time uninstalling all the stuff you don't need and installing
updates from Red Hat for the things you do need. Dell has pretty
good instructions on how to update the kernel and get the RAID
driver working.

With the exception of the kernel module for the RAID hardware
it's just like any other Red Hat server.

I see Dell is laying off another bunch of people today. I hope they
keep producing the servers. Hmmm, maybe I can get better
prices from them for hardware upgrades if they're short on
cash....