Parameter tape_size

The parameter tape_size always defines the physical tape size (tape length * write density).  The physical tape size is the total volume (in MB or GB) of the data that can actually be written to a volume without compression.  Consequently, different amounts of data can be stored on the same tape size, depending on whether you back up with or without compression.  Because BRBACKUP/BRARCHIVE takes this information into account, you never have to or should change the physical tape size if you use software compression or hardware compression (for tape devices with hardware compression).

·        If you require several tapes for your database backup, BRBACKUP uses the value of parameter tape_sizeto distribute the files for backup to the volumes.  During serial backups, the program makes sure that the physical end of tape is not reached.  During parallel backups, the program also optimizes the file distribution.

·        A single file should not be bigger than the tape size (possibly after compression).

·        When parameter tape_sizeis configured too small, the backup program will require more volumes than are actually necessary.

·        When parameter tape_sizeis configured too large, cpio will reach the physical end of tape. See cpio Continuation Tape.  In this case, it is essential that you correct the parameter value.

Guide values for tape_size for tape devices without hardware compression:

Tape type

Setting for tape_size

60 m DAT-Band/ 4 mm  DDS-1

1200M

90 m DAT-Band/ 4 mm  DDS-1

1800M

120 m DAT-Band/ 4 mm  DDS-2

3800M

112 m Video-Band/ 8 mm

2000M

112 m Video-Band/ 8 mm/ high density

4500M

3490 IBM-Band

700M

When using tape devices with hardware compression, you should always leave a reserve of around 200 MB for any errors in the calculation of the compression rate.  The compression rate is estimated based on an analogous software compression and is therefore not exactly the same as the actual compression rate of a hardware compression.

Guide values for tape_size for tape devices with hardware compression:

Tape type

Setting for tape_size

60 m DAT tape/ 4 mm DDS-1

1200M

90 m DAT tape/ 4 mm DDS-1

1800M

120 m DAT tape/ 4 mm DDS-2

3800M

112 m Videotape/ 8 mm

2000M

112 m Videotape/ 8 mm/ high density

4500M

3590 IBM tape

10000M

DLT 2000        10/20 GB

10000M

DLT 2000XT    15/30 GB

15000M

DLT 4000        20/40 GB

20000M

DLT 7000        35/70 GB

35000M

The estimation errors can be larger after a database installation, a tablespace extension, or a reorganization.  If the physical end of tape is reached in such a situation, you should reduce the value of tape_size by an additional 100-400 MB.

Make sure that the parameters required for using hardware compression are set.