On Mon, 20 Oct 2003, Kent Hauser wrote:
> Is it possible to backup a DOS partition (bootable) & restore it from a tar 
> file? I recently had a disk failure & used dump/restore on FreeBSD partitions 
> & made a tar dump of the DOS one. After "newfs_msdos" & "tar x", the 
> partition is not bootable. Is there a way to do this?

This is actually a really interesting issue.  The short answer to this
question is, "no."  The long answer is, "I don't really know.  Maybe."

There are two problems:  (Warning: it has been a very very long time since
I looked into this.  My memory could easily be faulty.)

 1) There are two very special files that have to be contiguos and at fixed
    locations in the file system: the msdos kernel and something else.
    The something else might have a name similar to "io.sys".  These are
    "hidden" system files.  To see them from MSDOS you have to specify a
    special DIR command option.  Normally these files are installed by
    specifying a special option with the MSDOS FORMAT command or by using
    a special MSDOS command (possibly the SYS command) that installs a
    copy of the basic OS from the currently running MSDOS system.

    There may also be an issue involving the MSDOS command interpreter
    program (which may be COMMAND.COM or some such thing).

 2) MSDOS files may have special attributes that don't map in any obvious
    way to traditional unix file mode bits.  These attributes tend to get
    lost when you read an MSDOS file system on unix or store MSDOS files
    in a unix style file archive (e.g. tar, cpio, ...).

Fortunately, most MSDOS files don't have any essential special attributes.
It might be possible to restore an MSDOS partition from a tar file and
then fix it up (make it bootable) with the SYS command when running off
an MSDOS floppy.

I make backups of my MS OS partitions by making raw copies in unix files.
(e.g. "dd if=/dev/ad0s1 of=/wherever/msos_backup bs=128k")
You can extract individual files from these backups by mounting pseudo
disk devices configured with the vnconfig program on FreeBSD 4.x (or
perhaps the mdconfig on FreeBSD 5.x).

Dan Strick
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