Re: [rdiff-backup-users] Tar replacement - format proposal

[Kevin Spicer]

On Fri, 2003-09-26 at 14:19, John Goerzen wrote:

> I don't see why this is true.  Presumably the per-file data embedded within
> the archive would contain all the information that a tape restore program
> would need, so it could just read the archive sequentially like tar.

Yes, I made that point later on in my post, that each block should
contain enough information to restore everything within it, and that the
index should be just an index.

> 
> However, even for tape, the central directory at the end of the file could
> be great.  Most tape drives can wind to a specific block far faster than
> they can read through the entirety of a file.  Even given the time lost for
> reading the central directory and the seeks necessary to do that, it would,
> in many cases, turn out far faster.

Thats a good point, how would the drive know where to find the index
though?  I'm guessing that you can skip to an EOF mark them seek back x
blocks from there, but how to know how many blocks the index uses...

Assuming that there are good answers to this (which I suspect there are
- I just don't know them!) I still think it would be a good idea to
permit writing a seperate index as well so that tapes can be searched
for the existance of file from an index on disk, rather than having to
load tapes until you find what you are looking for.




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