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...

The other method, (TSM's incremental forever) you simply restore the 1 TB
and you are done...
That is, TSM tracks all the data thus there is no need to lay down all those
incrementals that you won't use anyway.

The difference between the old way and the new way is simply the data base
to track all the information.

and remember, you really aren't going back to the very first backup with the
new way...
you are simply going back to ONLY THE DATA YOU NEED!
Tapes hold a LOT of data that can be accessed very fast (as compared to 20
years ago)
Current day tapes, drives, & ATL's can almost be viewed as old dasd when you
look at the capacities & access times.
So in our new way you just keep all the data out there ~somewhere~ and
simply ask for what you need when you need it.

Dwight



-----Original Message-----
From: Joni Moyer [mailto:joni.moyer AT HIGHMARK DOT COM]
Sent: Wednesday, March 05, 2003 8:21 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: progressive backup vs. full + incremental


Hello everyone!

I was wondering why the full + incremental would result in a longer restore
time than the progressive backup methodology?  From several co-workers
point of view they thought that it would be quicker on the full +
incremental because you wouldn't have to go back to the beginning backups
of the file and restore all of the incrementals, you would just go back to
the most recent full backup and apply the incrementals after that point.
When I went to explain the reasoning behind this, I had some problems
understanding the concept myself, so I was hoping someone could explain
both methods and why they differ in restore time and why progressive is
better than the full + incremental.  Thank you so much for any help you can
lend on this matter!



Joni Moyer
Systems Programmer
joni.moyer AT highmark DOT com
(717)975-8338