Re: A though on multi-session cds
Eric Kasten (kasten@nscl.msu.edu)
Thu, 7 Oct 1999 15:55:02 -0400 (EDT)
> On Thu, 7 Oct 1999, Steve Dodd wrote:
>
> > On Thu, Oct 07, 1999 at 09:59:54AM -0400, Eric Kasten wrote:
> >
> > > A thought on multi-session cds. I've been considering using CD-Writers
> > > as a way to create snapshots of certain types of critical data by
> > > writing a new track to the CD periodically (essentially creating a set
> > > of generation datasets on the CD). One of the down sides of this
> > > is that there isn't a particularily easy way (that I've located) to access
> > > the data tracks beyond track 01 -- ie, mount mounts track 01, but there
> > > isn't a way to mount a different track that also has an isofs on it.
> >
> > isofs in 2.3.x (for suitable values of x, certainly >=15) has a
> > session= parameter that you should be able to pass in via mount.
> >
> > What would be even more interesting is for cdrom block devices to make
> > multiple sessions appear as partitions -- assuming people don't ever put
> > _real_ partition tables on CD-ROMs, of course.
>
> I once used a multisession CD-ROM (don't recall the brand) whose authoring
> software and device driver allowed for incremental backups. The driver
> would present the multisession CD-ROM as one filesystem where you only saw
> the most recent version of a given file. It was pretty slick.
That would be a lot like having a CD-ROM filesystem that acted like an
inherited filesystem. Thus, you could do a backup on track 1 and then
incrementally write only the files that had changed to subsequent tracks.
When you mounted the CD-ROM you'd see only the latest versions of the
files that were backed up. I remember their being an IFS in the kernel
sometime ago, but it disappeared (I think (?)).
...Eric
Eric Kasten
kasten@nscl.msu.edu
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