[lbackup-discussion] Time point backup schema?

[henri]

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>> On a *NIX system (ie Mac OS X) additional disk space will be required
>> for the new or altered files.
>>
>> Most unaltered/unmodified files (resource forks and directories may
>> beehive differently) will consume no additional storage space on the
>> backup destination. However, because these files are hard links they
>> will consume inodes on the backup destination filesystem. The way all
>> of this works will eventually come down to the implementation of the
>> 'ln' command your file system and even operating system.
>>
>> In essence, LBackup will only require additional storage for new or
>> changed files. Files which have not been modified between snapshots
>> are hard linked (not re-copied) and therefore will not require
>> additional storage. Creating a hard link means that virtually no
>> additional storage on the backup file system will be required.
>>
>> The following URL will do a far better job of explaining the finer
>> points related to hard links : http://en.wikipedia.org/wiki/Hard_link
>>
> Excellent! :)
>
> So here is another related question about how it works to do the
> snapshot to those altered files.
>
> e.g. If I have a single file with the size of 10MB(for backup test
> only).
> I have slightly change one byte or one bit data at end of the file.  
> How
> much disk space will LBackup take for the next snapshot?
>
> As u know, rsync just backup file to latest version, which will  
> consumes
> one byte/bit of the diskspace. Of cause, it does NOT have a snapshot
> feature.
>
> Now, we just lower the network requirement with rsync, which is ideal
> for mirroring. So back to LBackup, how much space will LBackup takes
> with the next snapshot, which is a key point to disk management.
>
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Because two separate versions of the file will exist in the file  
system and they will not be hard linked, the old copy will consume  
10MB and the new copy will consume an additional 10MB + 1 byte/bit.  
This means that in total storage required for these two snapshots will  
be 20MB + 1 byte/bit.

LBackup currently has no support for this kind of delta backup/copy.  
There are other backup tools available if this is a feature which you  
require.

I am interested to know if some sort of delta copy is possible,  
perhaps though some sort of file system trickery or in some other way.  
This would be a great feature and under certain circumstances it would  
greatly reduce the required backup storage capacity. If I find someway  
to do this or if you know of some way to do this then that is  
definitely a feature to look at incorporating into the project.

As it stands this kind of delta copy is not supported by LBackup even  
though this feature will in certain circumstances dramatically  
increase the storage requirements for the backup.

Thank you for this great question!

I will add this feature request to the developer section of the  
LBackup site : http://connect.homeunix.com/lbackup/developer/

Thank you again.


PS : This message made it to the list just fine. Your assistance is  
greatly appreciated!