Evaluating Backup and Restore Time

How long your backup or restore takes depends on your database server configuration and the database size:

• The speed of disks or tape devices

  The faster the storage devices, the faster the backup or restore time.

• The number of incremental backups that you want to restore if a disk or system failure requires you to rebuild the database

  Incremental backups use less storage space than full backups and also reduce restore time.

• The size and number of storage spaces in the database

  Backups: Many small storage spaces take slightly longer to back up than a few large storage spaces of the same total size.

  Restores: A restore usually takes as long to recover the largest storage space and the logical logs.

• Whether storage spaces are mirrored

  If storage spaces are mirrored, you reduce the chance of having to restore damaged or corrupted data. You can restore the mirror at nonpeak time with the database server online.

• The length of time users are interrupted during backups and restores

  If you perform backups and warm restores while the database server is online, users can continue their work but might notice a slower response. If you perform backups and warm restores with the database server in quiescent mode, users must exit the database server. If you perform a cold restore with the database server offline, the database server is unavailable to users, so the faster the restore, the better. An external backup and restore eliminates system downtime.

• The backup schedule

  Not all storage spaces need to be included in each backup or restore session. Schedule backups so that you can back up more often the storage spaces that change rapidly than those that seldom or never change. Be sure to back up each storage space at level-0 at least once.

• The layout of the tables across the dbspaces and the layout of dbspaces across the disks

  When you design your database server schema, organize the data so that you can restore important information quickly. For example, you should isolate critical and frequently used data in a small set of storage spaces on the fastest disks. You also can fragment large tables across dbspaces to balance I/O and maximize throughput across multiple disks. For more information, see your IBM Informix: Performance Guide.

• The database server and system workload

  The greater the workload on the database server or system, the longer the backup or restore time.

• The values of backup and restore configuration parameters

  For example, the number and size of data buffers that ON–Bar uses to exchange data with the database server can affect performance. Use the BAR_NB_XPORT_COUNT and BAR_XFER_BUF_SIZE (IDS) or BAR_XPORT_COUNT and BAR_XFER_BUFSIZE (XPS) configuration parameters to control the number and size of data buffers.