Monday, March 26, 2007

Server specs - my kingdom for a 13amp socket

Warning: this might be quite a technical post.
One of the things we've been wondering about since we started offering schools Moodles is:

How many school Moodles can we expect to fit on a server?
Our current server configuration is specified as follows:
Web server:
Processor: Dual Intel Xeon 2.8GHz, RAM: 2GB , Storage: 4 x 72GB drives in Raid 5 configuration, OS: Windows 2000 Web server: IIS5
MySQL server:
Same as above without a web server.
this contains all of our 80 current school Moodles at learning.[schoolname].bucks.sch.uk - we have 20 more to go in soon.
With the increased takeup of Moodles by schools - particularly primaries but also secondaries coming on board, we've a need to move to a bigger number of servers to spread the load and provide enough capacity and space for growth - occasionally things are starting to creak on the servers. There are no clear guidelines for space and capacity - since by definition all schools will use their learning environments in different ways which will have different space and processing requirements. Does one secondary Moodle equal ten primary Moodles? Probably not, but no-one really knows - nor should they really. Atomwide's plan is to go with a 3 to 1 ratio of web servers to MySQL servers, with 50 Moodles on each server. However, as the guys at Atomwide point out, it's not the number of Moodles, it's the level of usage that makes the difference. Oh, and I think that Atomwide might be the company referred to in this letter in last week's Guardian Link E-Learning supplement.
When we started this project most Atomwide servers were Windows, which was understandable since the user database which underpins everything - our Moodles, email, videoconferencing, etc. - is an MS-SQL database. I'm not sure, but it might be significant that when the new Moodle servers go in they'll be running Debian Linux using the Apache web servers, due to Hewlett Packard fully supporting Debian on their servers now, something that wouldn't have happened a few years ago. For those of you who like these things, here are the specs of the new servers:
Web server:
Processor: Dual Intel Xeon 3.6GHz, RAM: 3GB , Storage: 6 x 300GB drives in Raid 5 configuration, OS: Debian/Linux Sarge Web server: Apache 2
MySQL server:
Same as above except 4GB RAM,2 x 300GB drives in Raid 1 configuration and without a web server.
I'll be interested (though not many other people will be) to see if the performance of the new servers is faster - and whether that's due to one or more of a number of variables:
  1. running Apache rather than Microsoft's IIS;
  2. running Linux rather than Windows 2003 Server;
  3. running a slightly newer version of Moodle;
  4. running all of the above on newer hardware.

However, whatever hardware you're using, it all has one thing in common - the need for power. So, you can understand my frustration when, with Atomwide having commissioned the servers, all ready to go, there's now a "slight issue" at County Hall on the corporate side of things which is preventing them being put in. Somewhere in the bowels of County Hall is a machine room (actually, I think it's in the Old County Offices across the road) where the servers sit and... there aren't enough power sockets to plug the UPSs for the servers in. Really. That's it. Apparently various BCC electricians have been called and the responses are Hmmmm, not sure, we'll do it as soon as we can... a week Friday? (not a direct quote but you get the idea). I imagine if it was something important like - ooh, email for council employees - then it'd be done quick smart, but we (or schools, anyway) aren't that close to the top of the food chain - yet.

3 comments:

  1. It may turn out to go deeper than power sockets. That server will draw about 1 amp when at full cry, and a typical 11-slot cabinet is only supplied with 2 amps in total. The power supply cannot simply be uprated, because then the air conditioning would get overloaded from the additional heat output.

    We faced exactly these issues with the new Yacapaca server, and wound up having to move to a different data centre with beefier cooling provision.

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  2. Hi Ian,

    If you want metrics then try running some performance tests on both servers.

    Take a look at this video for "Using open source tools for performance testing" from Google:

    "http://video.google.com/videoplay?docid=-6891978643577501895&q=london+test+automation+conference

    They kind of state the obvious at the start but it gets better around 23 mins in.

    Cheers,

    -Andrew

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  3. Not that technical at all!!!

    A very interesting post to see what's going on behind the scenes. I assume that west sussex is a similar setup.

    If it's any help I (as one teacher) would expect next year to be putting up about 1GB of resources. I would expect students to be uploading to me in the region of 1-4GB of files.

    I doubt that other teachers would want 5GB available, but anything less than 1GB I would consider as an insult and unworkable. Hope that gives you some kind of figure.

    One thing that you didn't mention was bandwidth.

    For instance, if you have an flv that you want pupils to use that could be at least 20kb/s. Lets take a secondary doing the same starter at the same time in 5 classes. That's 20*30*5=3000=3Mb/s.

    At full DVD quality you're looking at 100 times that!

    So my question is far more if the servers can cope with 150 simultaneous requests for video.

    - I'm thinking especially about screencasts.

    Thanks for the post though - it was very useful to know.

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