Backup Devices for Large Databases (SAP Library - Database Administration (Oracle) with SAPDBA)

Backup Devices for Large Databases

The backup of large databases creates an extreme load, both on the system resources and on the backup device being used.

Some examples follow, as well as some orientation values for the hardware environment of the backup devices.

The backup should not be carried out over a network, but either to volumes in locally mounted backup devices or directly to hard disks.

Backup devices:

The maximum number of locally connected tape devices supported by BRBACKUP:

as of Release 2.1K/ 2.2E 50
as of Release 3.0A 255

Backup devices (for example magneto-optical media), which are addressed via an external backup program can be reached via the interface program BACKINT (see External Backup Programs for Large Databases).

BRBACKUP/BRARCHIVE do not support tape jukeboxes. However, you can address such devices via the BACKINT interface to external backup programs.

The following backup devices are the most common: 4 mm (DAT DDS-1, DDS-2) or 8 mm (video).

However, these devices should only be used to backup large databases where there is no other option, due of the low tape capacity and small throughput. Experience shows that for a database backup of about 500 GB, about 100 tapes would be necessary. The backup time would also greatly exceed 12 hours, even with 20 tape units running in parallel.

Tape units with a larger capacity and higher throughput rate should be used if possible.

The following examples are not a representative selection of the available backup devices.

IBM 3490

Throughput with backup: about 5-10 GB per hour

Tape capacity: about 2 GB per tape

These devices offer high throughput, but relatively low capacity. These would only be useful if a tape jukebox were used, running an external backup program, for example, via the BACKINT interface

IBM 3590

Throughput with backup: about 5-10 GB per hour

Tape capacity: about 20-30 GB per tape

These new devices from IBM have promising technical possibilities. However, there is little practical experience available, as these devices are not yet very widespread.

DLT (Digital Linear Tape)

Throughput with backup: about 3-6 GB per hour

Tape capacity: about 10-15 GB per tape

If a throughput of 3 GB per hour is assumed for 20 tape units in parallel, the backup of a 500GB database could conceivably run within 12 hours on less than 50 tapes.

The numbers given in the examples are based solely on the abilities of the backup devices. However, other factors also play a large role, for example, the throughput values of the computer (in particular, hard disk access times, system bus speed, I/O (SCSI) bus speed). As a result, the total throughput decreases significantly. Do not mount too many backup devices on one I/O bus, so as not to overload it. If hard disks and tape units are mounted on the same I/O bus, you must expect the load to be split between the two.