Five into two does go… virtually!

Last week Ben Green completed a large job which has seen our inventory of servers at St Werburghs Community Centre drop from 5 to 2 machines.

Bristol Wireless recently consolidated a whole stack of servers into two new boxes using Linux-Vserver technology. We hope to save power and time, whilst providing a much faster service with better redundancy. Vserver is a kernel patch that allows one machine to appear to be any number of “virtual private servers”, which appear to become computers in their own right.

The pictures (courtesy of Ben Green) show the stack of redundant kit and two new servers – called Yin and Yang (Yang is on the left in the picture).

“Once upon a time when someone wanted to run something on a server at Bristol Wireless”, said Ben, “we used to say ‘go and find a box from the scrap computer pile and install an operating system on it’. Each box took power, gathered dust and generally got in the way. The boxes would fail and need re-building. The whole process was a real faff.”

“With our new Linux-Vserver install a new virtual server can be installed with just one command and it takes about 2 minutes,” he continued.

Ben says that creating new virtual servers is easy, but he wondered how could we duplicate our old services without extensive re-installation. However, he discovered this turned out to be as easy for most servers as moving all the files across and starting them up as virtual servers.

The LTSP suite took a bit more messing, with the services it was running needing access to some low-level resources not normally allowed for a standard vserver. However, the flexibility of the Linux-Vserver permissions system meant this was as easy as adding a list of needed resources and reboot the virtual server (which, unlike a real machine’s install, takes about 20 seconds).

Thanks to a lot of hard work and the invaluable support from the Linux-Vserver community, all five old servers could be moved to one box running Debian GNU/Linux. The second server is intended to help us split out LTSP services and keep all our terminals going in event of a hardware failure, but currently it just mirrors the other server ready to step in if there is a problem. Around 15 terminals run from the new server, so it’s crucial to have a drop-in replacement. In the past we haven’t had one, leaving us a bit vulnerable.

The original servers took about 800 W of continuous power to run. This is now down to 280 W and will get even lower when the motherboards in our new servers are made to use the power scaling features (omissions in the Asus BIOS don’t allow this at the moment). We expect to have the idling power use down to 180 W at that time. This is one fifth of the previous total.

The new servers run on dual core AMD FX-62 processors, which are jolly fast. Even with 7 virtual servers running on just one of these, all the services are much much faster. Compared to when we where using old boxes from skips to fulfil our server needs, the new box goes like a rocket. It’s much better for our developers and takes very little power for a new server, just a bit of RAM.

Ben has also done a technical write-up here.