Use
When backing up your Oracle database to tape or disk, you can use software compression. Use software compression only if you have no tape devices with
hardware compression. Using hardware and software compression at the same time does not improve compression rates.If you make remote backups over a network, using software compression significantly reduces the network load.
Features
Software Compression and Remote Backup to Parallel Tape Devices
You can use multiple tape devices when you use software compression or make a remote backup to a remote host. This means that unattended backup of large databases is possible even if you do not have a tape device with hardware compression or want to perform remote backups.
If several tapes are required for a backup with software compression or for a remote backup, the existing tape devices are used in parallel, assuming that the number of parallel copy processes was not reduced by changing the
exec_parallel parameter. The tape devices must be defined in parameters tape_address and tape_address_rew.Size of the Compression Directory
When software compression is used (
compress = yes, backup not on disk), BRBACKUP uses the compression rates to determine the space required in the compression directory. The free space must be at least as large as the largest compressed file. The calculated compression rates are stored in a detail log and in the database table SDBAD.For more information, see
Logs for BRBACKUP, BRARCHIVE, BRRESTORE and BRCONNECT.When BRBACKUP is started for the first time, compression rates are not available. In this case BRBACKUP uses internal default values that are usually smaller than the actual compression rates. For successful compression, make sure that the compression directory has at least as much free space as the largest database file needs before the compression.
If you specify
compress = only (determine the compression rates), no disk space is required in the compression directory. The sizes are evaluated by reading the compressed files directly (using redirection). As a prerequisite for this, the redirection character ">" must be used in the parameter compress_cmd (as set already by default).Example
backup_dev_type = tape|pipe|tape_auto|pipe_auto|tape_box|pipe_box
tape_address = (/dev/rmt/0mn)
tape_address_rew = (/dev/rmt/0m)
compress = yes
tape_size = 18G
See also:
backup_dev_type tape_address tape_address_rew compress tape_size