[Box Backup] Backup the backup

[Simon Lundström]

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On Nov 1, 2006, at 10:13 AM, Chris Wilson wrote:

> This is very difficult. Whenever the client is using the remote  
> server, the local server is more up-to-date than the local one.  
> rsync will not realise this and will happily overwrite the new data  
> with old. If you try to do an incomplete sync, for example telling  
> rsync not to overwrite newer files on the secondary server, you  
> will end up with a mess on the remote server.

 From man rsync:
-u, --update                update only (don't overwrite newer files)

I thought that was going to work, but maybe not?

> I can't think of a way to make this work reliably with existing  
> tools. The only possibility is some very complicated two-way sync  
> mechanism or replicating filesystem between the local and remote  
> servers. I would certainly hesitate to do something so experimental  
> as a primary backup solution, and I would test it very heavily.

Maybe unison http://en.wikipedia.org/wiki/Unison_%28file_synchronizer% 
29 is the way to go?

> Why not have the client back up to the local server even when it's  
> on the road? You should have plenty of download bandwidth on those  
> sites (more than the client has upload bandwidth) and it avoids  
> this problem completely.

Because many of these companies are small and don't have a lot of  
bandwidth since they only surf and check their mail they can't only  
use remote backup but needs local backup. (5-10 ppl transmitting  
2-10GB over 2Mbit can be come quite slow. I will only use lazy mode,  
i.e. backups will not be automatic. Besides not all clients can have  
servers or ports opened in their firewall.

- Simon
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