Rick,
As a preliminary step please ensure that hardware compression is supported by the device you are using.
When using compression it is important to remember that the 2:1 compression ratio frequently assumed or stated in technical documentation is an ideal and seldom reached as a practical average.
Some files compress better than others. Text files are probably the most compressible files in general while high density graphics files like files with .jpg, .gif, .zip, or .cab extensions are not likely to compress at all. Also, many programs, including some database and mail programs, already compress the files they control.
The incorrect media capacity problem is usually observed on tape devices which do not have Media Capacity Checker functionality. Generally, for most of the tape devices, this functionality is initiated from the firmware of the tape device. Even though the tape capacity is reported incorrectly, during the backup operation, the entire media capacity should be consumed.
Media capacity is calculated based upon past experience, once a tape has been read from beginning to end via backups to the tape and then when the tape is overwritten afterwards; or from a long erase or full catalog job.
Hence we request you to perform an erase operation on the tape and check. Also perform a full backup until the tape is filled for example if the tape capacity is 160GB then perform a backup of 160GB with overwrite option. Once the backup is completed and next time when the tape is inserted for backup, check the media capacity displayed.
Download the latest VERITAS device drivers for backup Exec v9.1 from the following
http://seer.support.veritas.com/docs/273853.htm
Please update the drive firmware to the latest.
To diagnose the cause of issue please cross-check the compression ratio from Windows 2000's native backup utility (ntbackup) with hardware compression(if supported by tape device)enabled. Select the same type/amount of data to backup and observe the result.
The following can also affect hardware compression:
1. The tape drive may be trying to compress data that is already compressed. If the data cannot be compressed any further than it already is, the attempt may cause the data to expand. Run a test backup with no compression to compare how much data can be written to the tape media without compression. When using hardware compression, software compression should be turned off, and vice-versa.
2. The system may not be able to keep up with the tape drive. If data is sent to the tape drive at a rate that is either slower or faster than the rate at which the tape drive can write the data to the tape, then the tape device must stop and wait for the computer. Each time the tape drive stops, it writes tracks of undefined data (gap tracks), repositioning the read/write heads for the time when more data becomes available. This causes the tape drive to stop and restart frequently, affecting tape capacity.
3. The tape media may be ready for retirement. When tapes are written to for longer than what the manufacturer recommends, an excessive number of rewrites can occur, causing a reduction in performance and tape capacity. Use a new tape to test compression and confirm that the media is the correct type for the tape drive.
For further information, please refer the technote below:
Technote:
http://seer.support.veritas.com/docs/199542.htm
Above technote is for Backup Exec version 8.x but you will get relevant information from it.
Hope this helps.
