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Thread: Backup datafiles size in RMAN

  1. #1
    Join Date
    Dec 2000
    I have 2 identical databases, about 39G in size, that we perform cold backup to disk using RMAN. I notice the backup file size for db1 is about 12G and db2 is 23 G. I don't understand why they are so different, only the fact that db2 has more transaction activities. Here is my cold backup script.

    8> run {
    49> # Cold database level 0 backup
    50> allocate channel d1 type disk;
    51> allocate channel d2 type disk;
    52> allocate channel d3 type disk;
    53> allocate channel d4 type disk;
    54> backup
    55> incremental level 0
    56> tag cold_db_bk_level0
    57> filesperset 5
    58> # Recommended format
    59> format '/backup/cold/PSTEST8/bk_%s_%p_%t'
    60> (database);
    62> # now that the backup is complete, open the db.
    63> #sql 'alter database open';
    64> }

  2. #2
    Join Date
    Dec 1999
    North Carolina
    Since there are more transactions in db2, fragmentation or empty blocks in between the data blocks may be the reason for different file sizes. If you take block level incremental backups, then you may get the same size backup files.
    Check for fragmentation or for empty blocks. See how many blocks a table is taking in both the databases.

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