Most present tape drives include a function called hardware compression. This makes data compression available to the magnetic tape by a drive. In many cases, this feature may prove very useful.
Features of Hardware Compression
The hardware compression is much faster than software compression because, as opposed to software compression, it does not use a computer processor which draws from resources. Also, it is transparent to the operating system, and data is compressed “on the fly.” Usually, the compression ratio for magnetic tape drives is 2:1. This means that if we would write 2MB data to a tape, then the drive will compress the data, and you will have only 1MB saved of compressed data on the tape. Sounds good, yes? But not really!
In fact, the compression ratio of 2:1 may be really equal to 1.2:1 or 1.6:1 or another ratio. That depends on the type of data that you are writing onto tape. For uncompressed data types (such as txt, bmp, etc.), the real ratio may be near 2:1. Still, if you are going to write pre-compressed data (for example, multimedia data types such as mpg, jpg, mp3, etc.), this ratio will be very poor and in some compression algorithms may cause the written data to tape to be larger than the original data.
For example, a tape that is LTO-4 (Linear Tape-Open 4 generation) has a native capacity of 800GB. If the compression ratio is 2:1, then the compressed capacity is 1600GB (in theory). If you do not use hardware compression, then with LTO-4 tape, you can write 800GB maximum. When you use hardware compression, you can write more than 800GB. How much? It depends on your data.
The compression ratio is also related to the speed obtained during operations on magnetic tape. This speed is greater when the compression ratio is better. For example, the tape drive has a native speed of 120MB/s. With 2:1 compression ratio of this speed is doubled. Also, in this case, the real speed is dependent on the extent to which data will be compressed.
Typically default hardware compression is turned on, but this is not a set rule. If a compression functionality for your drive is not enabled as “default”, you may turn on it in a few ways depending on the drive. Sometimes you can switch it on by an extra jumper on the corpus or through a program via the operating system.