Re: [rdiff-backup-users] Finding/designing a tar replacement

[Kevin Spicer]

On Thu, 2003-09-25 at 00:17, Ben Escoto wrote:

> Neat, that's a good idea.  The strategy of using volumes as file
> systems should be an important consideration.  I didn't even know that
> Linux could mount an iso image.  (How can I try this?)  

Using the loop option,
mount -o loop /some/file.iso /some/mountpoint

Unfortunately it only seems possible to mount read-only, if you want to
alter an iso you need to extract and rebuild though.

> 
> About extensions, the only iso9660 extensions I'm aware of are Joliet
> and Rock Ridge.  Neither will get you extended attributes and what
> not, but at least there existence suggests that iso9660 can be
> extended in a backwards compatible fashion.

I was slightly wide of the mark there, I remembered lots of options for
extensions in X-CD-roast, checking back I've found that they are
actually all settings for Rock Ridge / Joliet.  However, from the
mkisofs man page...

        mkisofs  is  capable  of  generating  the  System  Use 
        Sharing Protocol records (SUSP) specified by the Rock Ridge
        Interchange Protocol.   This is  used  to  further describe the
        files in the iso9660 filesystem to a unix host, and provides
        information such as longer filenames,  uid/gid, posix
        permissions, symbolic links, block and character devices.

> 
> Apparently the ISO standards are not public domain, but presumably
> enough information on iso9660 is out there somewhere.  Looking at a
> vague description of the format, it does seem that such a volume can
> be written before the lengths of the files are known, because the path
> table can occur after file data.  Can anyone confirm this?  Can CD
> burners burn in one pass?

I know you can use mkisofs to create an iso image without having to burn
it to CD, however I'm not sure if it is possible to pipe mkisofs to
cdrecord (I guess even if it were theres a risk of emptying the fifo and
making a coaster).

> 
> Also apparently the file size inside iso9660 is limited to 2GB.
> Finally I don't see any way of encrypting or compressing the entries
> in an iso9660 volume and still preserving the easy mounting
> ability.

There is a way of mounting a compressed filesystem, but I suspect it
requires a non standard kernel patch.  Apparently Knopppix uses it to
fit even more on their CD!

Thinking on this a bit more, maybe iso9660 isn't the way to go, you can
create just about any filesystem within a file (using loopback) [just
about all modern distros should support this, as its needed for initrd].
I suspect the two biggest issues would be streaming it onto a backup
device (not a problem where the device is a disk, but probably an issue
for tape and/or CDR) and portability (what other OS's support mounting a
filesystem image?)




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