Encrypting tape adds security, but it can also add significant costs if you attempt to encrypt your data before compressing it. Compression works by squeezing redundancy out of data, although encrypted data typically has very little redundancy to squeeze. Without compression, a typical backup requires between 1.5 and 2 times as much tape.
However, compressed data encrypts just as well as uncompressed data. Therefore, you should compress your backups before you encrypt them. The problem is that in most enterprises, compression is handled by the tape drives themselves. To make this approach work, you need to do your compression elsewhere.
If you encrypt your backups in hardware, this usually isn't a problem. Most encryption appliances, such as NeoScale CryptoStor and Decru DataFort, can compress data before they encrypt it. However, if you are using software encryption, you will need to use a separate data compression utility or a backup program with compression that will work with your encryption software. Many backup programs, such as Veritas Backup Exec, will compress data; some programs, such as SQL Backup from Red-Gate Software, handle both compression and encryption.
The good news is that the compression shouldn't slow down your backups. While encrypting to an acceptable level of security tends to be slow, compression generally isn't. If you handle the entire process in software, compressing the data won't add much, if any, time to the process.
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About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years, he has been a freelance writer specializing in storage and other computer issues.