Pieter Wuille wrote:
> 
>>> You're very right, and i thought about it too. Instead of using a RAID1 on
>>> the offsite backup, there are two separate backups on the offsite machine,
>>> and synchronisation switches between them. This also enables the use of
>>> rsync's --inplace option.
>> That should be safe enough, but doesn't that mean you xfer each set of 
>> changes twice since the alternate would be older?
> 
> That's correct, but it hardly seems to matter. Due to a problem the offsite
> machine was down once for over two weeks, and the subsequent synchronisation
> run still only took 14h. The limiting factor is the sequential read speed of
> the device, not the network.

Your network between sites must be exceptionally fast - that's probably 
not a typical situation.

>>> Catting the part files together to a device after transmission isn't a
>>> complete solution: what if the machine crashes during the catting...?
>> The machine crash would have to destroy the filesystem containing the 
>> chunks to be a real problem.  And then I wouldn't expect both your 
>> primary server and the server holding the file chunks to die at the same 
>> time, but it would mean you'd have to xfer the whole mess again. 
>> Perhaps you could alternate the catting to 2 different devices so you'd 
>> always have one ready to whisk off to the restore location.
> 
> Yes, i was wrong. A crash during the catting would normally not hurt the
> files that already were transmitted. As long as you don't start transferring
> the next set during the catting of the previous, there is no problem.

Maybe it doesn't matter if your network is as fast as your disks, but I 
like the idea of ending up with a disk you can ship overnight or toss in 
a briefcase and take to your disaster recovery location and start 
restoring immediately.

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com


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