[OpenAFS] how?: Distribute /home to n Terminal Servers

[Dan Pritts]

Several people commented on my "administrative hassle" assertion.

Primarily, this was based on the fact that with Steve's desired
configuration, he would end up with each machine in his cluster being
a critical point of failure (albeit a less critical point of failure
than a single NFS server), and thus each machine will require some
significant management, and if a single machine has a hardware failure,
then something has to be done about it sooner rather than later.

Compare this to a system with ten terminal servers and a pair of
clustered file servers.  When one of the ten terminal servers dies,
the load balancer steve mentioned will notice, and distribute the 
load to the other nine machines.  

since these are all identical machines, this is easy, and the machine
can be repaired at the convenience of the administrator. 

If we look at the likelihood of any single machine having a hardware
failure, we realize that by increasing our critical points of failure,
we are significantly increasing the likelihood of a failure that the
administrator will have to actually do something about in real-time.

We can protect against that by buying more expensive server-class
hardware for *all* the machines, at significant cost (say $3000 for
a decent server vs. $1500 for something with consumer-grade parts).  

Or, we could take that extra money, and spend it on a robust central
server cluster.  If we are talking two terminal server machines
it may not make sense.  If we are talking ten terminal server machines,
it almost certainly does.  

Additionally, distributing user volumes across a dozen file servers
would require administration - juggling volumes across file servers when
one gets too full, etc.  Sticking with a big server or would require
significantly less.

Nathan Rawling commented on the ease of managing AFS vs. NFS - he is
certainly right that once it is running AFS has a lot of manageability
plusses.  However, that comes with some significant overhead that
we in the AFS admin community tend to accept, and forget about.  

I get the impression that Steve is intending to send out a preconfigured
CD set for admins at schools to load on their clusters.  This suggests
that the end admin needs to have the simplest possible configuration.
I posit that a single (or clustered) (probably NFS) file server would
more likely provide that.

steve, I would love to hear more about who the consumers of your project
will be.  It sounds interesting.

danno

dan pritts                                       danno@internet2.edu
systems administrator                            734/352-4953 office
internet2                                        734/546-4423 mobile