OT: paging MAC expert(s) --- What's a Performa?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Nov 20 09:02:54 2001

This was misrouted and returned to me, I know not why or where ... Let's try
again ...

Dick
> -----Original Message-----
> From: Richard Erlacher [mailto:edick_at_idcomm.com]
> Sent: 20 November 2001 01:08
> To: classiccmp_at_classiccmp.org
> Subject: Re: OT: paging MAC expert(s) --- What's a Performa?
>
>
> If you're meaning operating on the tape contents, you're talking about weeks
> to
> months. The bits of a file are scattered around the disk, since it's random
> access, albeit in "clusters" or whatever you choose to call them, and in
> blocks,
> as the data buffer stores them, but unless you KNOW where the directory is
> in
> the bitwise image of the disk, and unless you know where all the pieces of
> the
> drive are to be found in the tape image, I'd submit it would be a mite
> tedious.
> The problem, of course, with image backup, is that the bits have to be
> extracted
> from the drive at the raw data level, i.e. with controller commands you
> normally
> don't deal with, and they can't be faithfully restored to a drive that's not
> physically identical to the one you started with, i.e. same number of heads,
> cylinders, sectors, etc, PHYSICALLY, else things fall apart, since we don't
> know
> how the drive firmware deals with translating from the block-level commands
> the
> OS may choose to send it, though it doesn't have to, to the buffers-full of
> data
> that the drive coughs up.
>
> Remember, when you restart the system, it has no OS other than what you can
> load
> from a floppy. IF that's the same, which certainly isn't the case under
> WIndows, as what you used to do the backup, then you're able, potentially,
> to
> deal with the data to be transferred to the newly cleaned drive in the same
> way
> that this particular OS deals with it. Of course, the OS doesn't know what
> you're doing, and doesn't know how to read the data on the disk, except as
> raw
> data, dealt with in buffer-fulls, and than only using the code you've
> written.
>
> Dick
>
> ----- Original Message -----
> From: "Christopher Smith" <csmith_at_amdocs.com>
> To: <classiccmp_at_classiccmp.org>
> Sent: Monday, November 19, 2001 4:00 PM
> Subject: RE: OT: paging MAC expert(s) --- What's a Performa?
>
>
> > > -----Original Message-----
> > > From: Richard Erlacher [mailto:edick_at_idcomm.com]
> >
> > > If your recorded "backup" is a bit-for-bit image of the disk contents,
> > > transferred to and from tape, there's no interpretation of
> > > the contents into
> > > files that can take place, is there?
> >
> > That's an interesting way to phrase this particular question, since the
> > contents are already in the form of "files" -- that is, if you ask the set
> > of drivers that got them to the disk in the first place. :)
> >
> > I believe it's possible (though it would be slow) to interpret a
> bit-for-bit
> > image directly on a tape and extract any given file, along with
> attributes,
> > etc. In fact, any operation that would be possible on a disk, in this
> case,
> > could be handled on a tape. The clincher is that it would involve a lot
> of
> > seek/rewind/seek/etc/etc..
> >
> > The underlying O/S need not even know the difference between the disk and
> > tape, except to know that the tape is removable (...that's not absolutely
> > required), and perhaps that it's incredibly slow.
> >
> > The worst that would be required is a device abstraction layer or the
> like.
> > You could write one yourself which would make the tape device "look" like
> a
> > disk device, for systems which don't have such a thing, and that would be
> > enough.
> >
> > How would you like to be able to mount your backup tape, and use a
> > file-manager on it? ;)
> >
> > > The Microsoft Backup that came with DOS, (a) never really was
> > > a backup, but,
> > > rather, was just a copy, and (b) never worked together with
> > > its "restore"
> > > function. Under DOS, copies were adequate, since the context
> > > didn't matter.
> >
> > If you mean that it didn't store attributes, or that sort of thing, you
> may
> > be right (never paid attention.) On the other hand, you're also right to
> > say that it wouldn't particularly matter under MS-DOS.
> >
> > Regards,
> >
> > Chris
> >
> >
> > Christopher Smith, Perl Developer
> > Amdocs - Champaign, IL
> >
> > /usr/bin/perl -e '
> > print((~"\x95\xc4\xe3"^"Just Another Perl Hacker.")."\x08!\n");
> > '
> >
> >
> >
>
>
Received on Tue Nov 20 2001 - 09:02:54 GMT