How Backup Exec for Windows Servers controls hardware compression on tape devices.
Backup Exec supports two types of compression for backups - software and hardware compression.
If hardware compression is selected to be used during a backup job, then Backup Exec issues a SCSI mode select command to enable hardware compression on the tape device to be used when the backup job begins. When the backup job is finished, another SCSI mode select command is sent to the tape device to disable hardware compression. If the backup job is configured to auto-verify then the SCSI mode select command to disable hardware compression is sent at the end of the backup and before the verify starts.
Actual compression is performed by the hardware, backup exec merely issues the command to switch it ON or OFF.
There are two methods that can be used to confirm that hardware compression is being enabled:
Method 1: Using SGMON:
To confirm that the process is happening, an SGMON log can be generated during a backup with hardware compression selected. Instructions on how to run an SGMON log are available in the Related Documents section below.
After running the SGMON log, look through the log looking for a time stamp that corresponds to the beginning of the backup. The job history log will display the time when the backup started. When the backup start time is found look for the following line:
"HARDWARE COMPRESSION ===> Compression is configurable"
This indicates that the tape device is capable of having the hardware compression turned on or off with SCSI commands. A few lines below this entry there will be another entry indicating that hardware compression is being enabled, that entry is shown below:
"HARDWARE COMPRESSION ===> Setting compression on"
Figure 1 is an example of what is shown in the SGMON log indicating that hardware compression is enabled:
Method 2: Using the SCSI Tracer Tool:
Tracer.exe will capture the SCSI compression commands that are sent to the tape device. See the following tech note for how to use Tracer to verify the compression Setting : http://www.symantec.com/docs/TECH50960