Backups Done During Multi User

[rsm%brl-bmd at sri-unix.UUCP]

From:      Robert S. Miles <rsm at brl-bmd>

Kirk McKusick's response to this question during the 4.2 BSD
File Systems Tutorial at the Toronto USENIX Conference last week:

	"If you want consistent dumps -- dump single user."

Because DUMP uses the raw disk and goes tracing along indirect
block pointers it can get confused if the file it is dumping
changes while the dump is in progress.  If a block which DUMP
believes to be an indirect block no longer has valid indirect
addressing data in it then the results are unpredictable.  This
is true of all the file system utilities -- their results are
not to be trusted when they are run on active file systems!

Therefore the safest way to do dumps is with the system down
(or at very least with the file system unmounted.)

				-Bob Miles, rsm at BRL