ADSM-L

Re: progressive backup vs. full + incremental

2003-03-06 04:28:12
Subject: Re: progressive backup vs. full + incremental
From: GUILLAUMONT Etienne <eguillau AT RGB-TECHNOLOGIE DOT FR>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Thu, 6 Mar 2003 10:24:25 +0100
I don't understand why collocation should use more tapes. Of course it
would be probably better to have one tape by client but if you manage to
backup for example 50 small clients on 20 tapes, you could use collocation
without buying more tapes. The difference would be that instead of backing
up each day all the clients on the last tape, resulting in each client
having files on each tape, it will put 2 or 3 clients on each tape. In
fact, at the end, you will probabbly have something like each client having
files on 2 or three tapes.
With full+incremental, depending on the regularity of your full backups,
you could have a client on far more tapes, tipically 1 full per week + 4
incremental.
With full+differential, you would have each client on 2 tapes, but the
amount of data backed up would be bigger because a file modified just after
the last full backup would be on each subsequent differential tape.
And in fact, as long as I know, most software based on full+incremental are
unable of collocation and use more tapes than TSM.
But in all cases, the most easy way to restore a full disk or a full
computer is to attach a single drive to this computer and make a full
backup of this computer each day. Most of my clients make that and in case
of a disk failure, everything is simple : you mount the last backup and
restore it completely. But if you need a single file .... and if you have
20 computers to backup ....



Etienne GUILLAUMONT
e-mail : etienne AT rgb-technologie DOT fr

RGB Technologie
Parc d'Innovation, Bâtiment PYTHAGORE
11 Rue Jean SAPIDUS
67400 ILLKIRCH
Tél :  03 90 40 60 60
Fax : 03 90 40 60 61


                                                                                
                                                                   
                    William Rosette                                             
                                                                   
                    <Bill_Rosette@PAPA        To:     ADSM-L AT VM.MARIST DOT 
EDU                                                                         
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                    05/03/2003 16:21                                            
                                                                   
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This progressive incremental confuses me.  This is what I thought was going
on:

1. Differential is all changes from last FULL backup.
2. Incremental is all changes from last ANY backup
3. Full is all files not matter change on backup.

We used to do Differential with Weekend Fulls.  During a restore we would
restore Full if file had not changed, and then the last differential for
the other files that changed.  We never restored more than necessary.  It
depended on the restore.  Restore 1 file was the same on Differential as
Incremental (most current or before corruption).  The problem comes when
you are restoring directories or a whole system as in DR.  In the
Differential Weekend Full world you would restore Full and lay on top the
last Differential and your done.  Always 2 restores was all and restores
flew since data was all together.

Now the TSM world has its own database with its own reclamation,
expiration, migration, collocation, and the works. Come restoring 1 file it
is the same as above.  Come restoring directories or whole systems it will
depend where all the data is.  Our case, if the restore is not far back we
have a quick restore, but the further back we go in date the slower the
restore because of the no-collocation and the data is spread over 100's of
tapes.  This seems to be the same as an Incremental that the TSM database
keeps track of every file from every tape.

Thus, the reason we did not use Incrementals before was 1. Restores were
long, 2. No database to keep track of all Incremental tapes, 3.
Differential & Full used less tapes, and 4. money.  I am still dealing with
the progressive incremental that progressively eats resources/money.  My
suggestion would be for reclamations to reclaim to a collocate status or
somehow keeping the data together as it gets older.  Right now I am
probably going to run FULLs just to keep my restores to a minimum since the
tape issue will hurt us if we collocate

If I am off, I would appreciate anyone that can straighten out my
backups/restores.

Thank You,
Bill Rosette
Data Center/IS/Papa Johns International
WWJD



                      Gianluca Mariani1
                      <gianluca_mariani@        To:
ADSM-L AT VM.MARIST DOT EDU
                      IT.IBM.COM>               cc:
                      Sent by: "ADSM:           Subject:  Re: progressive
backup vs. full + incremental
                      Dist Stor Manager"
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                      03/05/2003 09:47
                      AM
                      Please respond to
                      "ADSM: Dist Stor
                      Manager"






Progressive incremental backs up only new or changed files.  during the
initial backup the client  backs up all eligible files of course(full
backup). Subsequently, files are backed up again only if they are new or
have changed since the last backup. In TSMs case, a pointer to each version
of every file for every client is kept  in the database , so there is no
need for another full backup.
When  you  need to restore, you can choose the specific version of the file
or  point-in-time  to  restore,  and TSM will restore only  that particular
file or files. The approach used for full + incremental backups (NetBackup)
requires  an  initial  full  backup,  followed  by  regular  incremental or
differential  backups (usually once a day), with the complete cycle needing
a  full  backup  to  be  repeated on a regular (usually weekly) basis. This
backup  method  results in redundant weekly full backups of files that have
not  changed,  wasting  both  network  and  media resources. The multi-step
restore  process in this approach requires the software to restore the last
full  backup,  then to restore  incremental or differential backups  on top
of  that   in  order  to  recover the latest version of a file or an entire
system.  This  methodology  not  only involves restoring more data, it also
means  more  tape  mounts  and  tape  positioning and consumes more network
bandwidth all of which amounts to having longer restore times.



Cordiali saluti
Gianluca Mariani
Tivoli TSM Global Response Team, Roma
Via Sciangai 53, Roma
 phones : +39(0)659664598
                   +393351270554 (mobile)
gianluca_mariani AT it.ibm DOT com
----------------------------------------------------------------------------------------------------



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which the  whole  of the Corporation's Galaxy-wide success is founded
-their fundamental design flaws are  completely  hidden  by  their
superficial design flaws"...



             Joni Moyer
             <joni.moyer@HIG
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             05/03/2003             incremental
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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