[geeks] Dynamic files / filesystems?

[Joshua D Boyd]

On Thu, Jun 06, 2002 at 08:28:43AM -0400, Matthew Braun wrote:
> This is still a ways off but I'd like to solicit opinions:
> 
> I'm building my multimedia store around a 100Gb drive in a PC to house
> primarily my ripped CD collection. I'd like to use FLAC (since I'm more
> concerned about quality than space) but my plans still require access to
> mp3s. Rather than have 2 duplicate directory trees storing FLAC files in one
> and the mp3 version on the other and the subsequent management headaches and
> unnecessary space consumption, I was hoping to somehow have a dynamic
> filesystem where the mp3 directory tree is but a shadow of the FLAC
> filesystem, and all reads of the mp3 version of a song actually trigger a
> JIT transform of the underlying FLAC file to mp3.

A 100gb IDE drive?  Yuck.  23gig SCSI drives are dirt cheap.  4 will
cost less than 1 100gig IDE drive.  Granted, you will also need a few
scsi bays to put them in, but 2 internal drives and 2 in an external
case shouldn't be that hard to pull off.

Anyway, FLAC is good stuff.  But that transform you are proposing is
going to take some significant CPU power if you want it to be
realtime, but you probably realize that.
 
> Now the Mona (Modify-on-Access) filesystem
> (http://www.cse.nd.edu/~ssr/projects/mona/) seems to support this, but it
> looks like it's a research project and not exactly ready for prime time. Are
> there better ways to accomplish the same task?

Without looking at it, my first thought is that it being a research
project is only going to be a problem if it could possibly loose the
flac data. But, give me a moment, and I'll review their page.

OK, that is some interesting stuff there.  But, I wouldn't feel safe
using it.  Unfortunately, this is exactly the sort of thing where a
tool like perlfs would come in handy, but complaints against perl
aside, perlfs is still in pretty bad shape.

You could write you own NFS server.  There was an article in linux
journal a few years back about doing that for the purpose of creating
custom file systems.  In the case of the article, he was writing a
version control system as file system, but the code should be easy
enough to reuse to make a readonly NFS server that transforms FLAC
files to MP3 files.  RFC 1094 (http://www.faqs.org/rfcs/rfc1094.html)
would be a good place to start for such a task.  If you make it a read
only file system, I think most of the complexity disappears.


-- 
Joshua D. Boyd