Keeping ahead of Skewed Time
Skew. It’s a very strange term. “Neither parallel nor at right-angles” is the phrase that crops up a lot on those online dictionaries, which is at least loosely concordant with the three definitions I’ve been used to. First was my mother’s mannerism of dubbing anything misaligned as “skew-whiff”.
Second is Mr Honeyball’s tendency to describe different versions of the same product, say Windows 7 Home and Professional, as “skews” (“This skew has no media player” is what to say if you want to sound as if you’ve attended Microsoft product briefings). The third definition is to be found in an especially fateful Windows Server error message: Skewed Time.
If you see an Event Viewer error that claims “the clocks on the client and server are skewed,” then there are several things you may assume. One is that you’re in deep trouble. Another is that those first two usages of “skew” aren’t going to help a great deal in working out what to do next.
The last thing is that search engines aren’t going to be much help in finding a way out of the jam you’ve got yourself into, either. The nature of this jam takes a bit of explaining, so let’s take a look at the pre-disaster configuration of the network first. A customer of mine has a comparatively early installation of VMware Server for Windows, running on a cripplingly heavy and noisy HP ProLiant DL585 Storage Server inside a 64-bit Server 2003.
If you see an Event Viewer error that claims “the clocks on the client and server are skewed,” then there are several things you may assume. One is that you’re in deep trouble
The particular selection of guest VMs on this server are mostly survivors from the shipwreck of an earlier group of badly misconfigured core function servers: there was a domain controller, a terminal server and an Exchange server, which may sound like a heavy workload until you remember that, actually, domain controllers don’t do much thinking or shovelling of data.
They merely parcel out relatively small quantities of information, in a timely fashion, on request. Likewise, terminal server (or as we should now call them, Remote Desktop) VMs tend to be easy to build and fairly well behaved.
So this trio of VMs had been leading a pretty quiet, smooth-running life until now, except of course that the last one was an Exchange server.
Now, this product isn’t the raving, erratic, paranoid monster it used to be and, truth be told, this one had been humming along nicely until it came up against the disk size limit of the VM it inhabited. This motivated my client to ask what the next step was for its virtualisation?
Should it stick more disks into the HP server and carry on, or could the company take advantage of the leaps and bounds in servers over the past few years to go to a quieter-running virtual host, while moving the VMs across in a non-destructive way?
To handle this process we collectively chose a Dell PowerEdge 2950. I won’t spend many column inches on this, but note that it’s the third major version of the 2950 series, with SAS disks and twin quad-core Xeon CPUs.
With a suitably populated and divided RAID array, this machine offered four times the storage of the DL585 and twice the CPU count – a bit of a no-brainer combined with the Express licence for “real” VMware vSphere 4, which (a few months ago) would provide three virtual hosts with 20 guests for £385.