At 6:40 AM -0800 3/5/03, Cook, Dwight E wrote:
Old style Full+Incr (as it was some 15-20 years ago...)
Say you run weekend full with weekday incrementals.
Say on Friday, your environment goes down
You restore from your weekend full
You restore from your Mon incr (all the data on the tapes)
You restore from your Tue incr (all the data on the tapes)
You restore from your Wed incr (all the data on the tapes)
You restore from your Thu incr (all the data on the tapes)
You restore from your Fri Incr (if it had already run, all the data
on the tapes)
Now, if 75% of the data on the system changes daily, you just restored
475%...
So if the environment has 1 TB of data, you just restored 4.75 TB's
to get it back...
But there are smarter ways of restoring from full/incrementals, like
the way FDR does it in the MVS world.
Restoring a full volume from full/incrementals, it starts with the
LAST incremental and restores the volume table of contents
(equivalent to a directory) and all the files on the incremental.
Then it works backwards with each incremental and then the full. For
each backup, if the file is in the VTOC restored from the latest
backup, and it has not yet been restored, it restores it. If it's
not in the latest VTOC (meaning it was deleted after the backup), or
it's already been restored from a later backup, it doesn't get
restored. So at the end of the process, you have your volume
restored to the condition it was in at the latest incremental backup,
and no files have been restored repetitively or unnecessarily.
--
Matt Simpson -- OS/390 Support
219 McVey Hall -- (859) 257-2900 x300
University Of Kentucky, Lexington, KY 40506
<mailto:[EMAIL PROTECTED]>
mainframe -- An obsolete device still used by thousands of obsolete
companies serving billions of obsolete customers and making huge obsolete
profits for their obsolete shareholders. And this year's run twice as fast
as last year's.
