frozen image method (backup) (FIM)

Frozen image( FIM) is a backup technique in which a data set is"frozen". A distinction is made between split mirror, copy-on-write( CoW) and redirect-on-write( RoW).

The techniques used should be seen from the point of view that the storage space required for backing up and restoring databases is increasing rapidly and strains the resources for this. In addition to the enormous storage space requirements, unrestricted availability plays a particularly decisive role in the backup, which is then no longer guaranteed.

Mirroring is a technique with which databases are stored simultaneously on two separate hard disks. The original data is stored on one hard disk, while an exact copy is stored on the other. Mirror splitting means separating the primary copies of the database from the secondary ones. The advantage of a split-mirror snapshot is that all the data is present on the mirrored disks. Whenever the utility runs, a snapshot is taken of the entire data volume, not just one of the new and updated data. This allows for offline access to the data, which facilitates recovery, duplication or archiving.

Another procedure for the Frozen Image is Copy-on-Write. This procedure optimizes the number of copies and avoids unnecessary copies and their storage. In contrast to mirror splitting, the copy-on-write procedure takes snapshots of the changes to the stored data and does so whenever new data is added or older data is updated. This procedure allows for much faster recovery of data in the event of disk write errors or other faulty functions. However, all previous snapshots must be available.