SUMMARY: dump uncertainty

From: Fred Hoare (
Date: Wed Jul 29 1992 - 06:25:18 CDT

Hello sun-managers

Thanks to everyone who replied to my posting.

My original post:
>The question I have concerns doing level 0 dumps. According to the manual,
>it is recommended that the disk be unmounted before doing a level 0 dump.
>Is this really necessary? What about doing other level dumps?
>I would like to use cron to automatically schedule dumps and don't want to
>inadvertantly unmount a disk when a user is logged onto the system. I have a
>SS2 running SunOs 4.1.2.

Most of the replies I got said that in theory the filesystem should be inactive
when doing a dump. This is because of the way dump works. It first does a
pass through the filesystem mapping the directories and files before writing
to tape. If the filesystem changes between the mapping and the writing there
could be problems. However most of these people also said that in practice they
never did this. Most dump the filesystem in the middle of the night (3am
seemed to be a popular time) when the system is inactive using cron.
Most also said that they had never had any problems doing things this way.
A few people said that if the data I was saving was critical then I should
do the dumps on an inactive partition.

Several people suggested using a package like Sun's Backup Copilot or Apunix's
Mdump as these automatically lock the filesystem during the dump process.
Michael Sullivan suggested getting the source code for dump and applying patches
called the "Purdue live file system" which causes dump to skip files that are
being modified with a warning message.

Raymond Ballisti sent the following:
        it is no good to dump a partition if somebody is using it.
        To try to reduce the problem I wrote a script which try
        to umount the partitions. To do this I ask the users logged
        in to logout (I mean, the procedure do this). Also batch
        jobs are stopped and so on. In this way the file system
        is quiscent while dumping. Everything is restarted at the end.
        If you would like to have a look, the procedure is on a
        file called dump_job (because is executed by cron) on
        ftp anonymous in directory src on my server "sirius"
        {deneb:ballisti:[ray]:33}% ypcat hosts | grep sirius sirius timehost mailhost sirius-gw
        Have a look. Suggestions for improvement are welcome.
I haven't had a chance to look at the script yet.

Torsten Metzner sent me a copy of a very long summary that was posted in April
on this subject. It included several scripts for doing dumps when booting
into single user mode. Thanks Torsten.

What I have done is to do my dumps in the middle of the night using cron.
15 minutes before the dump I use wall to tell users that a dump is about to
take place and that any files modified after that are not guaranteed to be
backed up. I do a level 0 dump once a week (Sunday night) and level 9 dumps
from Monday to Friday. I consider this to be adequate backup for our system.

Thanks to the following people who replied. (Daniel Strick) (Ian MacPhedran) (MaryHelen Donnelly)
era@niwot.scd.ucar.EDU (Ed Arnold) (Donna Koechner-G) (Mike Beaman) (Rand S. Huntzinger) (Russ Poffenberger) (Chuck Meares)
lemke@MITL.COM (Kennedy Lemke)
Chris Keane <chris@rufus.state.COM.AU> (Richard Amick)
Paul Allen <>
David Stewart <>
Michael S. Maiten <msm@Energetic.COM>
Steve Elliott <>
trdlnk!mike@uunet.UU.NET (Michael Sullivan) (Raymond Ballisti)
Dave Mitchell <> (simon beard)
Mike Raffety <>
Christopher Carpinello <>
Torsten Metzner <> (Jim Knutson)
Sandra Scott <> (Cynthia Eldridge)
ldavis!woden!gunn@snowbird.Central.Sun.COM (David Gunn) (System Administrator) (John Baird)

Frederick Hoare                email:
Image Processing Laboratory
Department of Electrical and Electronic Engineering
University of Cape Town,  South Africa

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