[OpenAFS] R/W replication

Dirk Heinrichs heinrichs@qis-systemhaus.de
Wed, 14 Feb 2001 08:46:13 +0100

Derek Atkins wrote:
> I doubt that RW clones will ever happen.  It would imply huge
> consistency issues.  Who's job is it to make sure data is consistent
> across all the servers?  In the current model, data is "pushed" from
> the RW volume to the RO clones by a sysadmin (or a cron job).  You
> would need more immediate data consistency with multiple RW volumes.
> Worse, you also have really hard race conditions.  For example, what
> if two clients are writing to the same file on different servers?  Who
> wins?  How do you let the clients know that there was a conflict?
> Mind if I ask to what purpose you want replicated RW volumes?  You
> certainly don't need to replicate user's homedirs.  And most system
> software should be RO anyways (you _do_ realize that you can still
> mount the RW volume of a replicated RO volume in order to make changes
> to the volume?)
I understand that implementing true RW replication has to deal with lots
of problems.

The reason I asked was that in case of inavailability of the "master"
volume, clients cannot save their changes. There could also be another
solution, that in case the server of the RW volume goes down, one of
it's RO replicas will automatically be switche to RW, as long as the
original volume is down.


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