How do we judge RMAN volumetrics?

Question

The following is my RMAN configuration:
CONFIGURE RETENTION POLICY TO REDUNDANCY 1; # default
CONFIGURE BACKUP OPTIMIZATION OFF; # default
CONFIGURE DEFAULT DEVICE TYPE TO DISK; # default
CONFIGURE CONTROLFILE AUTOBACKUP OFF;
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '%F';
CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET; # default
CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default
CONFIGURE MAXSETSIZE TO UNLIMITED; # default
CONFIGURE ENCRYPTION FOR DATABASE OFF; # default
CONFIGURE ENCRYPTION ALGORITHM 'AES128'; # default
CONFIGURE ARCHIVELOG DELETION POLICY TO NONE; # default
CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u01/app/oracle/product/10.2.0/dbs/snapcf_ccs21dev.f'; # defaultFrom above, you can see that neither compression nor optimization is set.
One of my data-files is over 6GB.
ccs21dbint/u03/oradata/ccs21dev(304)$ du -sh *
  39M   arch
  31M   control01.ctl
100M   index_a.dbf
5.0M   redo01a.dbf
5.0M   redo02a.dbf
100M   stats.dbf
480M   sysaux01.dbf
400M   system01.dbf
ccs21dbint/u03/oradata/ccs21dev(305)$ cd /u04/oradata/ccs21dev
ccs21dbint/u04/oradata/ccs21dev(306)$ du -sh *
  31M   control02.ctl
5.0M   redo01b.dbf
5.0M   redo02b.dbf
6.3G   table_a.dbf
1.3M   temp.dbf
1.0G   undorbs1.dbfHowever the backupset where it is backed up to is very small at just 1.40GB.
RMAN> list backup;
List of Backup Sets
===================
BS Key  Size       Device Type Elapsed Time Completion Time
27      35.24M     DISK        00:00:02     23-MAR-11
        BP Key: 27   Status: AVAILABLE  Compressed: NO  Tag: DAILYBACKUP
        Piece Name: /u02/flash_recovery_area/CCS21DEV/backupset/2011_03_23/o1_mf_annnn_DAILYBACKUP_6rn1wknh_.bkp
  List of Archived Logs in backup set 27
  Thrd Seq     Low SCN    Low Time  Next SCN   Next Time
  1    460     369109105  22-MAR-11 369109436  22-MAR-11
  1    461     369109436  22-MAR-11 369109808  22-MAR-11
  1    462     369109808  22-MAR-11 369111467  22-MAR-11
  1    463     369111467  22-MAR-11 369116485  23-MAR-11
  1    464     369116485  23-MAR-11 369120962  23-MAR-11
  1    465     369120962  23-MAR-11 369126753  23-MAR-11
  1    466     369126753  23-MAR-11 369131659  23-MAR-11
  1    467     369131659  23-MAR-11 369136775  23-MAR-11
  1    468     369136775  23-MAR-11 369141920  23-MAR-11
  1    469     369141920  23-MAR-11 369142168  23-MAR-11
  1    470     369142168  23-MAR-11 369142348  23-MAR-11
BS Key  Type LV Size       Device Type Elapsed Time Completion Time
28      Full    1.40G      DISK        00:00:53     23-MAR-11
        BP Key: 28   Status: AVAILABLE  Compressed: NO  Tag: DAILYBACKUP
        Piece Name: /u02/flash_recovery_area/CCS21DEV/backupset/2011_03_23/o1_mf_nnndf_DAILYBACKUP_6rn1wop4_.bkp
  List of Datafiles in backup set 28
  File LV Type Ckp SCN    Ckp Time  Name
  1       Full 369142353  23-MAR-11 /u03/oradata/ccs21dev/system01.dbf
  2       Full 369142353  23-MAR-11 /u04/oradata/ccs21dev/undorbs1.dbf
  3       Full 369142353  23-MAR-11 /u03/oradata/ccs21dev/sysaux01.dbf
  4       Full 369142353  23-MAR-11 /u04/oradata/ccs21dev/table_a.dbf
  5       Full 369142353  23-MAR-11 /u03/oradata/ccs21dev/index_a.dbf
  6       Full 369142353  23-MAR-11 /u03/oradata/ccs21dev/stats.dbf
BS Key  Type LV Size       Device Type Elapsed Time Completion Time
29      Full    30.95M     DISK        00:00:03     23-MAR-11
        BP Key: 29   Status: AVAILABLE  Compressed: NO  Tag: DAILYBACKUP
        Piece Name: /u02/flash_recovery_area/CCS21DEV/backupset/2011_03_23/o1_mf_ncsnf_DAILYBACKUP_6rn1ygmx_.bkp
  Control File Included: Ckp SCN: 369142376    Ckp time: 23-MAR-11
  SPFILE Included: Modification time: 22-MAR-11
BS Key  Size       Device Type Elapsed Time Completion Time
30      7.00K      DISK        00:00:02     23-MAR-11
        BP Key: 30   Status: AVAILABLE  Compressed: NO  Tag: DAILYBACKUP
        Piece Name: /u02/flash_recovery_area/CCS21DEV/backupset/2011_03_23/o1_mf_annnn_DAILYBACKUP_6rn1ymy3_.bkp
  List of Archived Logs in backup set 30
  Thrd Seq     Low SCN    Low Time  Next SCN   Next Time
  1    471     369142348  23-MAR-11 369142381  23-MAR-11How does this happen? Is there some other Oracle/RMAN setting that I'm overlooking?
I vaguely remember autoextend to maxsize confusing the hell out of Solaris (du command) but cannot quite put my finger at it.
Thanks.

Answer 1

Hi Sharma,
One of my data-files is over 6GB.
However the backupset where it is backed up to is very small at just 1.40GB.
How does this happen?If you query dba_segments and sum the amount of bytes you will see you have only around 1.4GB of segments the rest is freespace.
Can you post the output of:
select sum(s.bytes)/1024/1024/1024
from dba_segments s
/Rman wil only backup used blocks when backing up in a backupset mode.
This explains the difference in size.
Regards,
Tycho