[Box Backup] lazy and snapshot together, file formats and files changing often

[Chris Wilson]

Hi Louis,

On Fri, 16 May 2008, Louis-Dominique Dubeau wrote:

> I'm currently testing and evaluating boxbackup.  I have three questions:
> 
> 1.  Is it possible to set up boxbackup to have a client perform both 
>    lazy backups and snapshots of a single set of files, to a single 
>    backup store?
> 
> e.g. Boxbackup would generally be in lazy mode except that once a day it
> would perform a snapshot.  The only thing changing between the two kinds
> of backups would be the lazy vs snapshot mode.  All other parameters
> would remain the same.

Yes that's absolutely fine. The only difference between lazy and snapshot 
modes is that in lazy mode, bbackupd automatically performs a sync at 
regular intervals, whereas in snapshot mode, it only does so when asked. 
You can run in lazy mode and request snapshot syncs whenever you want.

> 2. It is possible to access the backup store outside of boxbackup?
> 
> What I mean is that if the store was a collection of .tar.gz files
> encrypted with gnupg, then I would just need gnupg, tar and gunzip to
> peek at the contents of the store.  Is the backup store created by
> boxbackup like this or does it have some sort of boxbackup-specific
> format?

Not really, because the individual files are encrypted and stored in a 
format that allows them to be diffed while encrypted, and there is no 
standard for such a format that I'm aware of, there exist no tools other 
than Box Backup that can process these files.

Having said that, it wouldn't be hard to modify bbackupquery to read and 
decrypt the encrypted files itself, without using the network. Encrypted 
directories would be a little harder.

> 3. As a small quick and dirty test, I've set boxbackup to perform lazy 
>    backups my ~./mozilla directory.  I figured there are enough changes 
>    in there to trigger lazy backups.
> 
> Anyway, I found that some of the files in the cache maintained by
> firefox are not backed up even after several hours.  Then I thought that
> maybe files which change too often are never backed up.  The way I
> understand lazy backups, boxbackup waits until a file has remained
> unchanged for some time before it backs it up.  So if the file changes
> too often maybe that time period never elapses and the file is never
> backed up.
> 
> So can it happen that a file which is frequently changing never gets
> picked up by a lazy backup?  Must I force a snapshot at some point?

No, there is a MaxUploadWait parameter which specifies after how long the 
client will give up waiting for the file to be quiescent and back it up 
anyway. However, it's more likely to be in an inconsistent state when this 
happens, as the application may not have finished writing to it.

Cheers, Chris.
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