Peter Walter wrote:
> 
> As a Linux newbie, I have only a partial understanding of the technology 
> underlying Linux and BackupPC, but I get the impression that the problem 
> with a rsync-like solution is that processing hardlinks is very 
> expensive in terms of cpu time and memory resources. This may be a 
> stupid question, but, if hardlinks are the problem, has any thought been 
> given to adding to BackupPC an option to use some form of database 
> (text, SQL or otherwise) to associate hashes to files, instead? It seems 
> to me that using hardlinks is in fact using that feature of the file 
> system *as* a database, a use that does not appear to be optimal ... if 
> I have misunderstood, please educate me :-)

Using the filesystem to back up files is pretty much optimal for the 
operations that backuppc actually does.  That is, creating a new link 
will atomically succeed or fail regardless of how many other processes 
try the same thing at the same time and the link count is always 
maintained correctly in the corresponding inode.  Name lookups are 
fairly efficient operations, and the free space list is always 
maintained correctly.  Disk head motion (the usual bottleneck) isn't 
always optimal but nothing else is going to do it any better.

The place it isn't optimal is when you try to do other operations on the 
archive filesystem like reconstructing it with a file-oriented copy 
mechanism that has to traverse all the filenames and match up the inode 
numbers to duplicate the hard links.

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com


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