ADSM-L

Re: How to force PENDING to EMPTY/SCRATCH immediately?

2000-11-03 11:42:34
Subject: Re: How to force PENDING to EMPTY/SCRATCH immediately?
From: Serge Gaudet/EIG <Serge.Gaudet AT ECONOMICALINSURANCE DOT COM>
Date: Fri, 3 Nov 2000 11:10:05 -0500
Remember that:  If you have REUSEDELAY set to 7, you are preserving the
validity/usability of 7 DB backups volumes (assuming 1 generation a day).
The DB backup tracks where the files are.  When a reclamation is done, the
data is not moved... it is copied.  When you force a pending volume to
become empty, and decide to use it to backup new data right away, you may
be putting your business recoverability in jeopardy!!!!!  The latest DB
backup knowns where the latest copy of your files are, but the previous DB
backup only knows where the previous copy of the files reside.  The
"Pending" state is a representation to show that the tape will soon be
available for re-use, but could be needed if a less than 7 days old DB
backup is to be referenced.

Scenario: You set REUSEDELAY at 0 - you recall released tapes - you backup
new data on those recalled tapes - Disaster strikes (you went outside for a
smoke, and a meteorite flattened your building!!!) - You rush to a recovery
site with your vaulted tapes - You prepare to recover your environment from
your vaulted tapes and latest DB backup - The recovery site's tape drive
chews your most recent (offsite) DB backup..... -  You change tape drive,
and restart your recovery with your day old DB backup - Now, to recover
your file, TSM needs to refer to the previous copy of your files... off the
tape you already overwritten!  You're doomed! (you business is doomed, and
you are likely out of a job for good...  )

REUSEDELAY should not be tampered with just to recall tapes when you're
running out of tapes.  You would be better to buy more tapes for a spare
stash in case you run out of the rotating tape supply (i.e. those emptied
tape TSM releases and returns to you at the time they are recalled from
offsite vaulting).

I find REUSEDELAY's value to be sufficient at 3 for most environment.
Remember to "SET DRMDBBACKUPEXPIREDAYS".  It should be the same as your
offsite storage pool's REUSEDELAY.  It insures the recycling of the DB
backups match the recycling of the reclaimed tapes that are no longer
expected to be referenced.

Serge Gaudet, CMI
Consultant





                    "Rushforth, Tim"
                    <[email protected]        To:     ADSM-L AT VM.MARIST DOT 
EDU
                    PEG.MB.CA>                  cc:
                    Sent by: "ADSM: Dist        Subject:     Re: How to force 
PENDING to EMPTY/SCRATCH
                    Stor Manager"               immediately?
                    <ADSM-L AT VM.MARIST DOT ED
                    U>


                    02/11/2000 06:11 PM
                    Please respond to
                    "ADSM: Dist Stor
                    Manager"





Check for message ANR1341I in the Activity Log.  Based on the times in our
log, it appears to be an hourly check that is done.

Eg. Tape becomes pending on Oct 25 at 12:05, becomes Scratch on Nov 1 at
12:54 - reuse delay set to 7 days.


Tim Rushforth
City of Winnipeg
trushfor AT city.winnipeg.mb DOT ca