Les Mikesell wrote at about 14:23:06 -0500 on Tuesday, June 2, 2009:
 > Jeffrey J. Kosowsky wrote:
 > > >  > We already do have the issue of different optimizations for different 
 > >  > filesytems - and databases are even worse.
 > >  > 
 > > 
 > > Pick one or two database implementations that work on multiple
 > > platforms. Problem solved.
 > 
 > Yes, but you'll inherit the worst properties of both the database and 
 > the filesystem it sits on.
 > 
 > > Les, I understand that BackupPC as-is works perfectly for you on
 > > ZFS/Solaris.
 > 
 > It works well enough on ext3/Linux, which is what I'm actually using.  I 
 > think it might be even better on ZFS.
 > 
 > > However, you need to recognize that some of us have
 > > different setups and different needs. Just because you don't need an
 > > SUV for your transportation needs doesn't mean you can convince me
 > > that I don't need an SUV for my different transportation needs. Maybe
 > > it's even true that a database approach would measurably degrade
 > > performance (though I doubt it) but that doesn't mean that the
 > > tradeoffs of better flexibility, extendability, and transportability
 > > aren't worth it for other people.
 > 
 > I'm just being pragmatic. Backuppc generally works.  Linux is not 
 > difficult or expensive to obtain, nor is opensolaris.  Filesystems that 
 > support hardlinks aren't hard to find. There are ways to deal with 
 > copying filesystems.  When someone writes the database version I'll try 
 > it out, but right now it's all talk and not particularly convincing. 
 > While there are some theoretical points you can make about the attrib 
 > file, I can't recall anyone ever mentioning problems with it on the 
 > list. Nothing in my experience tells me that maintaining a database and 
 > a filesystem that need atomic synchronization is going to be better than 
 > a filesystem alone in any way that I care about - or that I would be 
 > able to trust files and database entries copied separately to another 
 > system. There are other places that could be bigger improvements in my 
 > opinion - for example in handling large growing files or storing 
 > additional attributes.

For me the biggest limitation is that it doesn't store extended
attributes and ACLs. I have looked (briefly) into extending that
functionality and in fact it was that effort that led me to think that
a database is the way to go. Otherwise adding additional attributes to
the attrib file just seems kludgey since there is no good general
purpose way to store/access them. Plus, the more attributes you store,
the slower it all will become since you will still in general need to
read in and unpack the entire attrib file to find just one piece of
information. Then my thinking was that once you start rewriting it all
in an abstracted objected-oriented fashion then you might as well go
the next step and store it in a database rather than having to
re-create all the database-like functionality.

The second limitation that has been discussed ad-nauseum is that hard
links make it difficult to move, copy, or split the pool across disks.

The other advantages that I mention then come along mostly for the
ride once you implement a database backend.

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