dumping active file systems

[Ross Parker]

In article <10239 at cbmvax.commodore.com>, grr at cbmvax.commodore.com
(George Robbins) writes:
> In article <384 at vela.acs.oakland.edu> schemers at vela.acs.oakland.edu
(Roland Schemers III) writes:
> > Hello! I have a question about using 'dump'. How dangerious is it to
> > dump an active file system? That is, dumping a file system that is
> > mounted, and while the system is in multi-user mode? I have gotten
> > various replies from DEC, ranging from "It might corrupt the whole dump",
> > or "Only the active files will be messed up".

> There's no really good answer to this question.  If you want dump that
> are guarenteed to be restorable without hassle, do *all* of the either
> standalone or with the filesystem unmounted.
> 
> Many sites compromise by doing the critical (level 0, weekly) dumps in
> standalone mode and doing the daily incrementals while the system is up,
> ideally during a low activity time period.
> 

To put my $0.02 in, we perform weekly full and daily incremental backups
*always in multi-user mode* on 33 *IX systems at MPR. We have been doing
so for at least the 5 years that I've been here, and have *never* had an
occasion where something has been lost. At least, we've never been caught
missing a file - I'm sure our tapes have irretrievable 'holes' in them...

CAVEAT - Because of the nature of dump, I know that we've been *extremely*
lucky in this respect. If I could afford to take my systems down, I would
do all of my dumps single-user. We currently do our dumps starting around
5:00 pm, when the building is starting to get quiet. Our full dumps are
to 8mm tape, and are thus very fast, so the file systems don't change much
during the dump.

If you can afford to do it (I can't), it would be wise to dump in single
user mode. Tar is *not* a good alternative, as it's tape error handling
is nonexistant, and it will not handle every eventuality that a Berkeley
file system can throw at it.

Ross Parker				parker at mpre.mpr.ca
(604)293-5495				uunet!ubc-cs!mpre!parker