[OpenAFS] two replicated servers

[Derek Atkins]

matias morawicki <mmora@barcala.ing.unlp.edu.ar> writes:

> Hi all, I'm trying to set up a two servers configuration with replicated
> volumes. I want to be able offer the same resources (except homes) even if one
> machine fails. 
> I've both servers running normally with all volumes I want replicated, but I've
> read in the documentation that with this configuration (two servers) Ubik may
> fail if one of the servers is down, since the cannot elect the main server. Is
> that correct or I've misread something? Is it possible to have such a configuration?

This is true.  The machine with the lowest IP address get's an extra
half-vote in the quorum election, so if it goes down then you will
lose quorum.  The fix is to run with three database servers, because 2
> 1.5 (so even if your lowest-ip server goes down, you still have
quorum).

> Another thing. I'd like to have a semi-recent replica (one day old, one week
> old) of the home directories in case the main server fails, even if it's a
> read-only volume. I've been thinking that maybe it's possible to make a "vos
> release" of them daily (at midnight for instance) and configure the clients to
> "prefer" the main server (R/W volume) in normal situations. In this case, only
> if the main server fails I can use the "old" and R/O copy of the secondary server. 

You can do that..  Just be sure that the user homedir mountpoint is
specifically for the RW volume, otherwise it will decend into the
RO volume and really confuse your users.  So, me sure you use the -rw
option to fs makemount.

> I'm all ears. Thanks a lot.
> 
> Matias Morawicki
> Network Administrator
> Facultad de Ingenieria
> Universidad Nacional de La Plata

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
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