DB2 FP4, BackupCompression

[Eric Herber]

Does anybody have any further information regarding
the compress option for the db2 backup command introduced
in db2 V8.1.4 ?

I made several tests on a solaris 2.8 machine with db2 V8.1.4
and came to the conclusion that the compress option only seems
to influence backups going to disk, not to a storage manager
like TSM.

The 1st database (offline) backup was made without
specifying compression, i.e.:

db2 "backup databae sample use tsm"
Output from "dsmc query backup /SAMPLE/*":
* * * * * * *Size * * *Backup Date * * * *Mgmt Class A/I File
* * * * * * *---- * * *----------- * * * *---------- --- ----
API *82.710.528 B *09.02.2004 12:09:15 * *MC48 * * * *A
/SAMPLE/NODE0000/FULL_BACKUP.20040209120800.1

The 2nd database (offline) backup was made with
compression, i.e.:

db2 "backup databae sample use tsm compress"

Output from "dsmc query backup /SAMPLE/*":
* * * * * * *Size * * *Backup Date * * * *Mgmt Class A/I File
* * * * * * *---- * * *----------- * * * *---------- --- ----
API *82.710.528 B *09.02.2004 12:10:34 * *MC48 * * * *A
/SAMPLE/NODE0000/FULL_BACKUP.20040209120918.1

There is no difference in the size of the two backups.
Doing the same test but specifying a file system directory
as backup destination results in different backup sizes:

db2 "backup databae sample to /tmp/db2backup"

-rw-r----- * 1 db2udb1 *tivdba * 79712256 Feb *9 12:11
SAMPLE.0.db2udb1.NODE0000.CATN0000.20040209121110. 001

db2 "backup databae sample to /tmp/db2backup compress"

-rw-r----- * 1 db2udb1 *tivdba * 20992000 Feb *9 12:12
SAMPLE.0.db2udb1.NODE0000.CATN0000.20040209121142. 001

There seems to be no further explanation in the releasenotes
of fixpak 4. (I know that I could compress backups thru TSM
proprietary options).

Thank you for any input.

Best regards

Eric
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IT-Consulting Herber
Mobile: [phone]
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[Philip Nelson]

Eric Herber wrote:

Does anybody have any further information regarding
the compress option for the db2 backup command introduced
in db2 V8.1.4 ?

I made several tests on a solaris 2.8 machine with db2 V8.1.4
and came to the conclusion that the compress option only seems
to influence backups going to disk, not to a storage manager
like TSM.

The 1st database (offline) backup was made without
specifying compression, i.e.:

db2 "backup databae sample use tsm"
Output from "dsmc query backup /SAMPLE/*":
Size * * *Backup Date * * * *Mgmt Class A/I File
---- * * *----------- * * * *---------- --- ----
API *82.710.528 B *09.02.2004 12:09:15 * *MC48 * * * *A
/SAMPLE/NODE0000/FULL_BACKUP.20040209120800.1

The 2nd database (offline) backup was made with
compression, i.e.:

db2 "backup databae sample use tsm compress"

Output from "dsmc query backup /SAMPLE/*":
Size * * *Backup Date * * * *Mgmt Class A/I File
---- * * *----------- * * * *---------- --- ----
API *82.710.528 B *09.02.2004 12:10:34 * *MC48 * * * *A
/SAMPLE/NODE0000/FULL_BACKUP.20040209120918.1

There is no difference in the size of the two backups.
Doing the same test but specifying a file system directory
as backup destination results in different backup sizes:

db2 "backup databae sample to /tmp/db2backup"

-rw-r----- * 1 db2udb1 *tivdba * 79712256 Feb *9 12:11
SAMPLE.0.db2udb1.NODE0000.CATN0000.20040209121110. 001

db2 "backup databae sample to /tmp/db2backup compress"

-rw-r----- * 1 db2udb1 *tivdba * 20992000 Feb *9 12:12
SAMPLE.0.db2udb1.NODE0000.CATN0000.20040209121142. 001

There seems to be no further explanation in the releasenotes
of fixpak 4. (I know that I could compress backups thru TSM
proprietary options).

Thank you for any input.

Best regards

Eric

Eric,

In my experience, backups to TSM have been compressed automatically for some
time. You notice this if you use dsmadmc to monitor the number of bytes
being transferred, as compared to the number of bytes being stored. When
you restore a backup image from TSM it uncompresses as part of the process.

HTH

Phil

[David Mooney]

Eric Herber <er**@I-hate-spam.org> wrote:

I made several tests on a solaris 2.8 machine with db2 V8.1.4
and came to the conclusion that the compress option only seems
to influence backups going to disk, not to a storage manager
like TSM.

That should not be the case. The compression feature is completely
independent of the backup target.

One possibility for what are seeing is that the first thing that DB2
sends to TSM is an estimate for the size of the backup. (This helps
TSM make smart decisions for disk pooling, etc.) Of course, DB2 is
not able to predict how well a particular database will compress,
so it sends the complete uncompressed size as its estimate. It could
be that the 82MB that TSM is giving you as the size of the compressed
backup is the value that DB2 gave on its initial size estimate rather
than the actual size of the data that was eventually sent.

dave