Why are encrypted backups to tape larger than expected?
When I encrypt backups that are written to tape, it appears that more data is written to the tape or that the compression feature on the tape drive is not working.
The hardware compression feature on tape drives may not be able to compress encrypted data. This will give the appearance that more data is being written to the tape.
If you wish to compress the data before writing it to the tape, then use the "Compress backup data" option when configuring the job. This software compression will happen before the data is encrypted, allowing for the size of the data to be reduced before it is written to tape.
If you choose to use software compression, you may also want to disable the hardware compression on the tape drive. If not, you could possibly see a minor increase in the actual size of data written to the tape.
Software compression will use more CPU resources. Therefore, you may want to run this job when the system is in less demand.