Re: Does anyone shut down for system disk backup any more?

From: Carl Perkins (carl_at_nospam.gerg.tamu.edu)
Date: 11/07/03 

Date: 6 Nov 2003 18:24 CST

Mike Rechtman <michael.rechtman@hp.com> writes...
}Basic question has already been asked: If your system is critical enough
}to be up 24x365, then surely you should be _entirely_ sure of the
}quality of your backups, not 'reasonably' sure?
}Of course you could always restore a previous backup, and and one
}previous to that ... until you hit a good one, with a decreasing risk of
}failure. But it sounds inconvenient and open to error.
}
}Mike

You know thosee backup tapes you made by shutting down your system?
If you are _entirely_ sure that they are good, then you know nothing
about tapes and tape drives.

There is a distinctly non-zero chance that any given tape is not useable.
There is also a distinctly non-zero chance that your tape drive could mangle
the tape when you go to restore it. These things happen. Fortuantely
they don't happen very often.

There is also a distinctly non-zero chance that your tape is only readable
on the drive that created it due to alignment problems. This could be very
bad if your tape drive is repaired, replaced, or upgraded.

There are probably several more such factors than indicate that if you
are _entirely_ sure that those backups of yours are restorable then you
are ignorant of how reality works.

The odds of an /IGNORE=INTERLOCK backup being bad are small. Very small,
usually. If you use CONVERT/SHARE to make clean copies of SYSUAF and
other such files before running the abckup, the odds of the backup as a
whole being unrestorable are probably not significantly worse than the
odds of your "_entirely_ sure it is good" tape going bad or being shredded
by your tape drive or other such unfortunate events happening.

There are many factors to consider. I think that in most cases doing a
backup while the system is up is a very good plan. You should also get
clean backups by booting from the CD when it is practical to do so.

Backups that are slightly less reliable than those produced in the ideal
case are vastly superior to no backups.

If you can schedule down time for a "boot from CD" backup once or twice
per year, do you not think that it might be a good plan to at least try
to get backups in between those?

Do you avoid brushing your teeth between visits to the dentist because
brushing your teeth doesn't clean them as good as the dentist's
cleanings, or do you brush them anyway because "not as good" is a
lot better than "not at all"?

--- Carl

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