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A few words about hardware compression in a backup with tape drives.

Most present tape drives include a function called hardware compression.
This makes available data compression to the magnetic tape by a drive. In many
cases this feature may prove very useful.

The hardware compression is much faster than a software compression
because as opposed to the 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 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 saved only 1MB compressed data on the tape.
Sounds good, yes? But not really!

In fact compression ratio of 2:1 really may be equal of 1.2:1 or 1.6:1
or another ratio. That depends the type of data which you are writing
onto tape. For uncompressed data types (such as txt, bmp, etc.) real
ratio may be near 2:1 but if you are going to write pre-compressed data
(for example multimedia data type 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.

Magnetic tapes manufacturers provide two tape capacities. First – written
a large font – a compressed capacity and second – usually written
smaller font – a native data capacity. For example a tape that is LTO-4 (Linear
Tape-Open 4 generation) has 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 enable 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 corpus or through a program via the
operating system.

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