Backups and Restores

Fortunately, Informix now only has two backup/restore options - ontape and onbar. The onarchive utility no longer exists and for many this was a positive improvement.

The onbar utility allows multiple dbspaces to be archived in parallel. The archive can be divided by dbspaces, not database, and could be run with one tape drive for each dbspace.

As the number of parallel onbar backups increase so the elapsed time required for the archive decreases. The aim is to produce an archive schedule that minimises the restore time i.e. the number of separate tapes [level 0,2,3 and logs] that must be applied, but at the same time has the minimum impact on the overall system. This might mean running the daily backup during normal working hours if the overnight data processing schedule is resource hungry.

If the backup window is not large enough to backup the entire system then half could be archived on day 1 and the other half on day 2. Alternatively, the high activity dbspaces backed up daily and the low activity dbspaces weekly. The use of differing levels of backup can also be included.

Remember that the key for a fast restore is to apply as few logical logs as possible. The application of logical logs is the slowest part of the restore process. Restoring archive tapes is a much quicker process since pages are simply read from tapes and written to disk with very little logic involved.

To improve archive performance:

• Use faster tape drives.
  
  
• Examine the physical layout of disk and tapes on the SCSI chain. Will an archive flood the SCSI bus degrading the rest of the system?
  
  
• Use tape striping if available. Tape striping is same as disk striping, the archive writes to a single logical tape drive made up of a number of physical tape drives.
  
  
• If you have enough disk space, consider writing the archive to disk first, then copying it to tape later. Disk access is much faster than tape access.