How to make a disaster boot floppy?

Norman Kohn nvk at ddsw1.MCS.COM
Fri May 25 22:05:01 AEST 1990

In article <187 at> john at (John Weald) writes:
>In article <9005202304.aa13994 at PARIS.ICS.UCI.EDU> baxter at zola.ICS.UCI.EDU (Ira Baxter) writes:
>>Having installed a tape drive, and snapped a copy of my disk onto a
>>tape,  I am wondering how to restore that image should my disk
>>contents get wiped out.  Since one has to custom-configure ISC Unix
>>to install the tape drive, the obvious solution is to install
>>a fresh Unix, configure it, and then restore the tape.... This
>>solution suffers the problem of having to do all that configuration
>>work, when the desired result of it is already sitting on the tape,
>>just waiting to be restored.  Clearly a chicken-before-the-egg? problem.
>>Surely there must be a better way; I'm open to suggestions.

After having tried under uport 386 the solution of making a new
unix kernel on the floppy that reads the tape, I settled on
the following scheme. Its advantage is that disaster recovery
is simple, the "supplement" disk is readily updated, and
you don't need to keep multiple flavors of boot floppy around
(when the vendor upgrades the os, there's minimal extra work)

1) boot off standard boot disk.  In the unusual event that the
hard disk is totally clobbered, rebuild at least the minimal
unix partitions with the vendor's script.  Modification
of the script is a reasonable idea, but I haven't bothered.
It obviously helps to have reasonably current printouts of
/etc/partitions, /etc/fstab, and the mkpart listings of 
mkpart -tpa ...

2) use cpio to read in the new unix kernel, configured for your
tape drive.  I keep a floppy with /unix and the necessary /dev
files (also any essential /etc files, currently none) in cpio format.

3) save the /etc/partitions file created by rebuilding unix, as
it will be overwritten from tape.

4) do sync;sync; uadmin 2 0

5) reboot unix from hard disk
be sure now to mount any file systems that will need to be
mounted to read the tape, then save /etc/mnttab (a copy
will be read in from tape)

6) load from tape

7) ps_data will have been read from tape and should be cleared.

8) shutdown and reboot: the unix kernel on tape, which was
read in over the kernel you booted from, is probably newer.

9) file systems not needed for bootup and basic operation may
be easier to create at this point, when full unix facilities
are available.  I keep different file systems on separate
tapes (they require different backup algorithms and frequencies).
One benefit is avoiding splitting a backup over multiple tape
volumes.  That way I can run the backups unattended, and have
the tape automatically scanned via cpio -it to make sure
the files are all there and the tape reads to the end.
Backup and scanning, of course, are done via shell script.

Norman Kohn   		| ...ddsw1!nvk
Chicago, Il.		| days/ans svc: (312) 650-6840
			| eves: (312) 373-0564

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