Sybase 12.4.2 Eliminating data verification, Spooling backup data, Balancing system load, 416

Determining your data backup and recovery strategy

Eliminating data verification

You can also improve the speed of backup and restore operations by setting CRC OFF in the BACKUP command. This setting deactivates cyclical redundancy checking. With CRC ON, numbers computed on backup are verified during any subsequent restore operation, affecting performance of both commands. The default is CRC ON. If you turn off this checking, remember that you are giving up a greater assurance of accurate data in exchange for faster performance.

Spooling backup data

You may find that it is faster and more efficient to create backups on disk, and then spool them onto tape for archival storage. If you choose this approach, you need to unspool the data onto disk before restoring it.

Increasing memory used during backup

The amount of memory used for buffers during backup directly affects backup speed, primarily for tape backups. The BLOCK FACTOR parameter of the BACKUP command controls the amount of memory used. If your backups are slow, you may want to increase the value of BLOCK FACTOR for faster backups.

The effect of BLOCK FACTOR depends on your operating system, and on the block size specified when the database was created. By default, the database block size is 4096.

On UNIX, the default BLOCK FACTOR is 25. With this combination, BACKUP is able to buffer data ideally for most UNIX tape drives, with enough data in memory that drives are kept busy constantly throughout the backup.

On Windows NT, the default BLOCK FACTOR is computed based on the database block size. This value usually achieves maximum throughput on NT. Because of the way NT handles tape devices, you may not be able to achieve faster backups by increasing the BLOCK FACTOR.

Balancing system load

Adaptive Server IQ allows you to perform backups concurrently with all other read/write operations, except those that affect the structure of the database. It is still a good idea to schedule backups during times of low system use, however, to make the best possible use of system resources—disk, memory, and CPU cycles.

416