Software Compression

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.

·        Advantages

If you make remote backups over a network, using software compression significantly reduces the network load.

·        Disadvantages

Ў        High CPU utilization

Ў        Lengthy backups due to compression process

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 BR*Tools.

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

·        Device type:

backup_dev_type = tape|pipe|tape_auto|pipe_auto|tape_box|pipe_box

·        Tape device addresses:

tape_address = (/dev/rmt/0mn)
tape_address_rew = (/dev/rmt/0m)

·        Compression parameters:

compress = yes

·        Tape size:

tape_size = 18G

See also:

backup_dev_type

tape_address

tape_address_rew

compress

tape_size