Data compression

The aim of data compression is to improve utilization of the capacity of the volumes and consequently to reduce the number of MTC required for a saving data. FDDRL recognizes two types of data compression:

• Hardware compression
  Hardware compression is performed by the MTC device (i.e. the device controller compresses the data and optimizes blocking). It is performed automatically when the corresponding volume type is used (e.g. TAPE-C4). The data saved in this way can only be read on the corresponding MTC devices.

• Software compression
  Software compression was offered by FDDRL up to V15.0A if hardware compression was not possible (but had to be specified with the operand DATA-COMPRESSION=*YES). Since state-of-the-art MTC devices work with hardware compression by default, software compression is becoming increasingly less important for the MTC devices in use and is no longer offered in FDDRL V16.0A and higher. If this compression type is encountered during restoration, FDDRL automatically decompresses the data.

Irrespective of the type of compression, backup volumes can be duplicated without restrictions by means of PERCON (see chapter "Duplicating FDDRL backup volumes with PERCON" and the “PERCON” manual [11]).