ADSM-L

versioning / expiring / multiple backups under same nodename

2002-01-18 06:34:04
Subject: versioning / expiring / multiple backups under same nodename
From: "Warren, Matthew James" <matthewjames.warren AT EDS DOT COM>
Date: Fri, 18 Jan 2002 11:31:28 -0000
Hi TSM'ers,

(this ones a little long winded, sorry :)   )

I have a customer who wishes to assess the maximum risk he would incurr in
the following situation;


We have a copygroup for backup set for 31 day point-in-time recovery. We do
not have nolimit for any copygoup parameters - we assume there will only be
a single backup each day.


The customer has a 5 node cluster. 1 -> 4 are production machines, 5 is a
failover machine.

They would like to know the risk involved when, should a machine be failed
over to 5, they back up the data now visible to 5 under the nodename of 5
instead of the original machines nodename, & the original machine continues
to run a backup as well (this would only see local disk, as a portion of the
failed over machines disk is now visible to 5, and hence mark all the
non-visible files as inactive)

We have told them backups would become inconsistent within filespaces that
have the same names across machines, and showed them how fiddly it would be
to restore a machine if they had only had one failover occurr in a 31 day
period. They would like to know exactly what the risks are if they have
multiple failovers within a month, and have multiple machines backing up
same-named files under a single nodename!!

They won't take 'It won't work' as a answer, they would like to know how it
will impact the point in time restore capability for a particular machine,
if they keep track of what machines failed over when.

As far as I can work out with pen&paper, in a worst case, for a 3 machine
cluster where 1 & 2 can failover to 3 at any time, the maximum impact would
be to reduce the point-in-time restore capability for a particular machine
by the number of days that machines have been failed over to 3 in the last
31 day period, because files with the same path filename on machines 1 and 2
would expire early if they change more often on one machine than they do on
another.

I get a headache if I try and extend this to a 5 machine cluster.

do you other TSM'ers agree?

and, I know from our perspective this is a 'silly' thing to work out because
they should listen to the advice of the people that know & switch to backing
things up correctly, but they are insisting they have this info...

Any help is much appreciated!
Thankyou,

Matt.