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

[Nathan Rawling]

Steve,

> >*every* machine that wants to access files that live in /afs needs to
> >be an afs client.  This includes AFS server machines.
> >
>
> ok.  Since we have a small number of machines, what would be the
> situation running *all* (max 10) machines as AFS Servers, and then
> acting as their own clients,

My understanding is that you want to keep the number of DB servers down
because of performance issues when you have too many. I suspect that
probably three DB servers would be sufficient for your application. You
want more than one to eliminate your risk of a single point of failure,
two is not recommended for technical reasons, so three is a good bet.

With that said, you could run the file server portion on each of your
terminal servers if you so desire. If your prime goal is to distribute
load, that might be the way to go.

> >For your configuration, I woudl recommend a single AFS file & db server,
> >which may or may not also be one of your XDMCP servers (i would tend
> >to have it on a separate machine).
> >
>
> ok.  Will the clients still sync if the server is down ?  Will we still
> have our single point of failure ?  Can more, or all of the Terminal
> Servers act as OpenAFS Servers, as well as a client for the cell ?  Can
> we then `mount` this cell as /home ?

Well, with one server, you would definitely have a single point of
failure. As Dan Pritts mentioned, even with a multiple server solution as
I talk about above, a server outage would result in some user home
directories becoming unavailable.

As you spread the user volumes across more fileservers, you reduce the
impact of the loss of one of them. If you use every one of your terminal
servers as a file server, and you have 10 servers, you only lose 10% of
your user volumes if/when a server dies.

I have heard that Netapp has an implementation of NFS with working
read-write failover, and I know that Veritas has a solution. However, I'm
sure that either would charge big bucks.

> We simply want 2-10 Terminal/Application Servers that keep /home/* +
> UIDs + GIDs sync'ed at all times.  All these Terminal/App Servers are on
> the same physical Ethernet Segment, firewalled in, on one site, and
> probably in the same rack - although it would be nice to distribute
> across the complex/campus near their associated set of Terminals.

You should watch out for the technical limitations of AFS as a solution.
If you have users with files larger than 2gig, AFS is not probably the
best solution. Byte-range file locking is another common area of concern.

The largest administration hassle with AFS, in my experience, has been
managing the backups. The bundled backup system is cumbersome (although it
has probably been greatly improved since I last used it), so frequently
you have to work out a solution that matches your environment.

All of my experiences with AFS, both for large cells and tiny ones, have
been positive, possibly excepting the backup system.

Nathan