** Using WeBWorK **

We recently received the  following query.

Dear Prof. Gage,

I am an assistant professor in the Johns Hopkins University. We plan to
use WeBWork for some calculus courses, maybe eventually up to a scale 
of 500 to 600 students. Here we need your valuable help.

Now our IT guy wants to know how much space WeBWork may require for 
such a class, including the temporary files and data files, so that he can
properly configure the server. Will you please give us some estimates?

Thanks for your kind consideration!

Best regards,
Qiao

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Here's our answer:

Dear Qiao,

Mike Gage has forwarded your email to me. 

Thank you for your interest in WeBWorK. I'm sure you are aware that Johns Hopkins used WeBWorK for many years under the direction of James Martino.  Jim is still at Johns Hopkins but has moved from the math department to the Digital knowledge Center, an R&D unit in the Hopkins university library structure.  His email is jrm@jhu.edu .  You certainly should get in touch with him if you haven't already.  He can tell you what he ran the courses on at Hopkins. If you talk with Jim, say hi for Mike and I.

First you should have your IT guy look at http://webhost.math.rochester.edu/webworkdocs/discuss/msgReader$1572 which gives some important info.  Also have him look at http://webhost.math.rochester.edu/webworkdocs/discuss/msgReader$1808 which is interesting and gives more info. about people having load problems.  Note that in Arizona State's case their problem was due to bad hardware they hadn't noticed and in Dartmouth's case the problem was that someone wrote a (very bad) problem that did a tremendous amount of needless calculations.  But the comments on server configuration are still valid.

At Johns Hopkins you are not talking about many users but I would still try to use a dual processor server if possible.  Concerning disk size I'll give you some figures below but disk space is so cheap that I would certainly err on the large size. 

The basic WeBWorK system files will fit on 10 MB but if you want to turn the access log on (it's off by default) that can become huge maybe 500 MB or more.  The tmp files at Rochester need about 4-5 GB (we have twice as many users as you anticipate) --- note that we have them on a separate partition that is not backed up.  A course (with logs, DATA, many problem template) should easily fit in 50 MB but this assumes people compress the database from time to time.  Most professors never do this (it requires one click) so maybe 500 MB is a safer size.   Also professors should remove unneeded tmp files (again it requires one click) but most don't.  You can get by with a pretty small (by current standards) amount of space if you want to but it is definitely not worth the trouble.  I see Dell is charging $224.10 for a 36GB 10K RPM Ultra 320 SCSI Hard Drive and I'm sure there are cheaper venders.  That size would be more than sufficient for you. [Actually look on http://www.pricewatch.com/ where you can find good 73 GB drives for about $200].  I would give 2 GB for system files, 10 GB for tmp files (in a separate partition), and 10 GB for courses.   The system and courses don't have to be on separate partitions so you can combine them into one partition.  You can get by with a lot less but it's not worth your time to worry about it.

I hope this helps. Please fell free to contact us again.  Others may find this info useful --- would it be OK with you if I post this on http://webhost.math.rochester.edu/webworkdocs/discuss  ?

Sincerely,

Arnie

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Here is another sequence of queries and answers.

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On Thu, Nov 06, 2003 at 11:38:01AM -0500, Arnold Pizer wrote:
>
> You can get the fastest Dell 4600 with dual 3 Ghz Xeons and 2 GB of memory
> for about $6,000. This is one fast machine and might handle the load.  For
> $10,000 you can get an essentially equivalent (dual 2.5 Ghz Xeons but with
> larger cache) Dell 6600 but this gives you the option of adding two more
> processors.  That (a quad processor) would certainly handle the
> load.

    After checking the prices on this, it's not much more expensive to
add a second 2 processor 4600 system as it is to upgrade a 6600 to 4
processors.  I submitted specs to the chairman recommending two $7400
2650s with 3.2GHz Xeons, 4GB RAM, and 2 hard drives (RAID1), with the
idea of just adding or replacing them as distributed systems as time
goes on.

    I'll try load-testing by pushing all classes onto one server to
start with next semester, and as soon as I hear a complaint about
speed, I'll split them up between the two and mirror changed data
between the two nightly.

 I don't have the infrastructure for this
currently, but I'm looking into setting up Kerberos and AFS, moving
actual storage to other machines so I can do instantaneous failover if
something happens.  Do you know anyone who has done this before?

> I hope this info helps.  Please fell free to contact us again.  Others may
> find this info useful --- would it be OK with you if I post this on
> http://webhost.math.rochester.edu/webworkdocs/discuss ?

    Thanks, it gave me a starting point and a list of other people to
bug.  Feel free to post this, and if I forget to send you the results
of this by next July, feel free to send me e-mail asking.

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As mentioned earlier in the thread, we are servicing a fairly large number of students. I think we are over 4000 this semester. We have two machines - both dual processor pentiums, a 2.66GHz and a 2.40GHz. Earlier this semester, one of the machines was having hardware problems, so we had to shut it down and run off of just one.

Currently, we are running soley on the 2.66GHz machine, and that seems to hold up pretty well with the student load. Other variables which may be relevent to speed:

• We run dvipng only mode for displaying problems
• We use vlatex for quicker generation of pdf (faster than dvips and ghostscript - probably comparable to pdflatex)
• We run a hybrid somewhere between WW 1.8 and 1.9, but not 2.0 (yet)
• We cache images of graphs. Some of our problem sets are full of images (as many as 8 graphs in a single problem). They are much faster with graph caching.
• We keep dvipng/graph images for a week, but then delete them. Without that, we ran out of disk space and, well, it wasn't pretty. Of course, if an image is needed again, it is regenerated.

When we were having problems, I was shifting courses back and forth between machines. The course would be unavailable for < 1 minute in the process (disconnect course, tar it up, sftp it, untar, run script to fix permissions).

The biggest problem we ran into with this was that students/teachers would bookmark/link to the login script. When the course moved, those links were dead and students got the course not found error. Also, our main page of links to courses would change when we changed machines. In general that should not be a problem, but some browsers won't refresh a page even if the student shift-clicks on the refresh button (some versions of AOL). They got very frustrated. Even though it was clearly their browser's fault, they blame WeBWorK.

I don't synch course files between the machines. We have RAID mirroring on each machine, so even if it half-explodes, we should be able to recover.

John

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