Re: [rdiff-backup-users] Re: [Duplicity-talk] Pretty pictures and new version of proposal

[John Goerzen]

On Mon, Sep 29, 2003 at 08:06:08PM +0100, Kevin Spicer wrote:
> > fine with listing the archives in the old-fashioned (tar) way? Can most
> > tape drives even seek to the start of the index file at all?
> 
> I think that was the point of having two copies was so that streaming
> media could content itself with reading the data from the blocks, and
> not worry about having to somehow get the index

Yes.  The information should only be there.

> > For the sparse file support, I wonder if it might better to leave it out
> > and assume that anybody with large sparse files (and the common sense of
> > tofu) would think to encode the inner file with a compression method.
> 
> Thats fine, as far as storage is concerned, but doesn't that bloat the
> files when restored?  (I'm not very clued up on sparse files so
> apologies if I've missed something)

Yes; sometimes significantly.  Some platforms often use sparse files for
binaries, core dumps, and other things -- so they are more prolific than you
might imagine.  Imagine the hapless system administrator who finds that the
/usr partition is no longer large enough to hold his system files upon
restoring them from tape, though they're the exact same files that were
there before :-)

A sparse file is created on Unix systems by seeking past the end of the
file's data and writing data there.  The system does not actually allocate
space on-disk for the intervening blocks, and when read back later, simply
supplies a stream of NULLs for that area.

-- John