On 12/1/2011 3:21 PM, Long V wrote:
> Hi,
>
> I have set BackupPC to backup a directory where the content is always 
> wiped and re-populated with 99% of the time same filename and same 
> content inside the files. File timestamps would be different as they 
> have been re-generated.
>
> I expected that BackupPC would detect it's the same filename and same 
> content and use hardlink instead of re-copying the file again.
>
> However, I've been monitoring /var/lib/BackupPC/cpool using `du -sh 
> /var/lib/BackupPC/cpool` and it seems to be growing at a steady state 
> that is much faster than what I expected.
>
> Either I am not looking at the right pool or the way I measure the pool 
> size (du -sh) is wrong or BackupPC is not using hardlink in my case.
>
> To confirm my suspicions:
> - is  /var/lib/BackupPC/cpool the pool I need to look for
> - is `du -sh` the proper way to measure the size of the pool
> - how do I know how many hardlinks are pointing to the same file in the 
> pool?
> - how do I calculate the saving ratio of using hardlink vs simple copy 
> the file again? (this would confirm if my instance of BackupPC is 
> exploiting the saving advantage of hardlink or not)

The simplest way to determine if hardlinks are being used is to cd into
a backup directory under /var/lib/BackupPC/pc and run 'ls -l'.  The
number between the permissions string and the owner's name is the number
of hardlinks to the file.  In most normal directories this number will
be 1 for almost all of the files.  In a BackupPC backup directory, the
number will be at least 2 (pool and current directory) -- more if the
file is being hardlinked to other backups.

-- 
Bowie

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