[Box Backup] replicate two boxbackup servers

[Chris Wilson]

Hi Achim,

On Tue, 13 Oct 2009, Achim wrote:

>> If you want a multiple-master setup, have a look at:
>
> http://www.boxbackup.org/trac/wiki/FeatureRequests#a9Pseudo-ClusteringofServersfromBenon92704
>
> This Pseudo-Clustering of Servers certainly sounds like a very neat idea,
> and I understand that the required changes are not a "particularly
> significant amount of effort" (quoting Ben): the changes still need to be
> done at some point, right? This does not work out of the box.

I think it can be set up without changes to Box Backup, by replicating the 
user database between machines using rsync. Housekeeping on one server 
will temporarily prevent the client from backing up to another server, but 
it will retry and should connect next time. Increasing the housekeeping 
interval should help, especially bearing in mind that all the servers will 
run housekeeping independently, and running it three times as often as 
usual is unlikely to help.

The other changes Ben suggested are equally applicable to single-server 
systems, and not required to implement the solution as far as I can tell.

> Rsync however sounds like a neat idea, since you can run it every minute 
> (or every 10 minutes) to have a pretty recent copy of the pool. What 
> would happen to a file that is "in transfer" from the BB client to the 
> BB server during the rsync: will it be corrupted, or do files get saved 
> to the backup pool only after they have been fully received?

It will not corrupt the master file on the other servers, as changes to 
raidfile disk sets (even non-replicated sets) are written to a temporary 
file and then atomically renamed over the original. It will waste a little 
bandwidth, though.

Cheers, Chris.
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