[OpenAFS] Re: about failover - 2 servers (one "master" one replicas) - a bit long

[Vladimir Konrad]

Hello Andrew,

> > Cheers, I forgot to say _by hand_.
> You can do this with 'vos convertROtoRW', but it's intended to be more
> of a tool for disaster recovery (when you've permanently lost the RW,
> and all you have are ROs). Not generally for keeping up availability
> while a server is temporarily down.

> Note that if A goes down, you convertROtoRW on B, and A comes back up,
> you'll now have 2 copies of the RW. The one on B will be the one used,
> but A has another copy that may contain data you want. This can get
> rather confusing if you try to sync the VLDB with the list of volumes
> that are on each server.

Thank you, good to know this, it would be used as the last resort.

> Automatic failover has been done using multiple servers sharing the same
> backend storage; I don't think anyone's done it with separate storage,
> but we're not stopping you from doing so. You could in theory do
> something like that with some other HA software, and writing some
> scripts to issue 'vos' commands to do the conversions.

Cheers, it is quite possible some servers would get hooked into SAN,
so it is an option.

> But it's usually a lot easier if you can just treat RO volumes as
> high-availability, and RW volumes not.

Makes sense, it looks having multiple RW volumes would not scale that well -
writes would have to go to each volume, + synchronisation would get messy
I guess...

Thank you all, I have done the replicas.

Do I understand it correctly (observation), a read-only replica placed on
the same partition as the read-write volume does not "cost" much in terms
of disc-space? I have released few replicas and the disc usage did not go
up. Is it along the principle of LVM snapshots?

Kind regards,

Vladimir

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> because it reverses the logical flow of conversation + it is hard to follow.
>> why not?
>>> do not put a reply at the top of the message, please...

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