From: pds@analog.ingr.com (Peter Schachte)
Subject: Re: Disk Directory Manager
Organization: DAZIX, San Ramon, CA
Date: Mon, 13 Apr 1992 21:19:48 GMT

In article <1992Apr8.205812.14904@casbah.acns.nwu.edu>, tsarver@andersen.uucp (Tom Sarver) writes:
> In article <29E1057E.7049@ics.uci.edu> dkim@ics.uci.edu (D.Kim) writes:
> >I need to know if there is an utility for managing files and disks?  ...
> >Here are the features I want (and may not be possible in Amiga OS):
> >-virtual disk (VAD:) which acts as 1 big harddrive composed of floppy
> >	disks.  (about 500 DSDD disk equals 500 meg )

I posted a request for such a thing a few months back, and didn't get
any replies.

> >-HighDensity drive, other non-HardDrive scsi storage devices support

If you base it on volume labels, it should be quite possible to support
any sort of mountable removable media.  That is, your device or handler
tries to lock "ARCHIVE034:", and the system asks you to insert
ARCHIVE034.  Then you just insert the disk/tape/WORM disc/removable hard
disk/etc.  At least that's my understanding; I've only seen it work for
floppies.

> >-directories are stored in Hard Drive for speed and efficiency (simply
> >	they would be link to the physical files in the disks.)

I don't think this is a very good idea, because it locks the floppy set
to the particular computer and hard drive the directory lives on.  This
means you can't give your floppy set to anyone else, and if your hard
disk dies, you're in trouble.  And besides, you'll be occupying a lot
of hard disk for stuff you're not going to use very often.  The whole
reason I want this handler is to free up hard disk space.

You're probably not going to traverse the entire directory structure
very often, so the speed of going to floppy a few times (you cache the N
most recently used directory entries in ram, and hash individual
directory entries) is probably adequate.  With a two floppy system,
you'd keep the directory floppy in one drive, and swap data disks in
and out of the other.

> Yep, you'll need a handler if you want it to be accessible from the system
> transparently.  Here's how to get started:

["how to implement a file system" omitted]

I was going to implement this in a simpler manner:  keep the standard
file system on each floppy, and have each floppy contain as much of the
directory structure of the virtual device as needed for the files it
actually contains.  This means that the virtual device contains just
the union of all the files on all the separate disks.  So the directory
information is completely redundant, and can be recomputed by scanning
all the disks.

This approach has some advantages.  Firstly, it's pretty robust:  you
can get back any file that hasn't itself been corrupted.  Similarly,
you can loan one of your disks to another Amiga user, and he or she can
read it without any other disks.

It would also be possible, with a utility program that recreates the
directory from all the disks, to create a virtual disk from a bunch of
preexisting disks.  If you now have 500 disks full, I imagine this
could be quite an advantage.

If you do write or find such a thing, I'd sure like to use it!

-- 
-Peter Schachte
pschachte@analog.ingr.com
Newsgroups: comp.sys.amiga.applications