From: utzoo!decvax!harpo!floyd!cmcl2!philabs!sdcsvax!sdchema!donn
Newsgroups: net.unix-wizards
Title: Re: Flames on system backups
Article-I.D.: sdchema.495
Posted: Wed Apr 13 20:40:44 1983
Received: Mon Apr 18 20:15:54 1983

References: ittvax.670 uiucdcs.1842 ritcv.273 rlgvax.202

Although this has been quite an active discussion there are a couple of
points that no one has brought up.

Maintaining Multiple Filesystem Backups on One Tape:

We do this with our 4.1 BSD software on our VAX 11/750 on a daily
basis, without the need for "restor F".  We use different strategies
for short and long dumps.  Short dumps are those that don't use
multiple volumes; in particular our day and week dumps are usually so
short that all the dumps for all the filesystems fit on one 2400 foot
tape.  To make these we just have a shell script that dumps each
filesystem onto the no-rewind hi-density tape device.  Multi-volume
dumps get their own tapes.  We have had problems in the past where an
entire box of tapes was unacceptable for dump using 2400 foot
estimates; we just told dump to try shorter estimates for a week and
went to a different brand of tape thereafter.  (Why settle for less?)

Restores from multiple-file tapes are done with job control and the
"mt" program.  When restoring individual files you just:  use "mt fsf
nnn" to move forward nnn files to the file that contains the dump you
want to look at; start "restor x" on your files; stop "restor" with ^Z
when it asks you to mount the tape volume; use "mt" to reposition the
tape after it rewinds; then continue "restor" and it will find your
file(s).  You can be clever and have "restor" use the no-rewind tape
device, in which case it won't rewind the tape:  use "mt bsf 1" to move
back to the previous file on the tape and "mt fsf 1" to return to the
beginning of the desired file.

Problems With Restoring Directories and Handling Tape Errors:

Kirk McKusick at Berkeley has changed "dump" and "restor" for 4.2 BSD
so that they act much more like "tar".  Dumping and restoring are both
faster; not by an order of magnitude but "about as fast as tar", due to
the improved filesystem layout.  You restore to a MOUNTED filesystem.
You can give directories as arguments and they will be recursively
extracted.  Files are always extracted under their real names, not some
inode number.  (In fact the inode number is no longer relevant, since
files are created using the normal file creation mechanisms even on
full filesystem restores.  This means that you can dump and restore a
filesystem to a SMALLER partition.) All your old tapes will be
compatible with 4.2 BSD even though the filesystem layout is completely
different.  If you get a tape error while restoring, the program takes
advantage of the (relatively) smart tape driver and the "redundant
information" which the manual entry talks about, and attempts to help
you.  And, best of all, the program is now called "restore"!  The only
disadvantage is that you will never get it to run without virtual
memory (or lots of memory period), so it is not portable to smaller
(dinky!) machines.  Latest projections for the first 4.2 tapes:
beginning of May(be).

Donn Seeley  UCSD Chemistry Dept. RRCF  ucbvax!sdcsvax!sdchema!donn
             (619) 452-4016             sdamos!donn@nprdc