There are two types of compression available for your backups - hardware and software. The hardware compression is usually enabled and disabled by either a DIPswitch or jumper on the tape drive. Please consult the tape drive manual to verify this. The software compression is enabled and disabled through the backup options within the software. It is recommended that you disable the software compression option if the tape device supports hardware compression. Hardware compression is far superior in speed and compression than the software counterpart.
It is not recommended to enable both hardware and software compression. This will cause the size of the data set written to the tape to increase in size; usually taking more space than the original data. The reason for this is because the software first compresses the data, adding header information for the software compression, and then the tape drive tries to compress the data. Unable to compress the information further, the tape drive still writes header information to the data set, thereby increasing the file size written to the tape cartridge.
About the author: Craig Konas is a senior member of NovaStor Corporation's Technical Support group. Craig has assisted thousands of customers with backup and disaster recovery during each of his 5 years with NovaStor. NovaStor technical
support is a free service to customers.
This was first published in January 2002