Why the tape media is mostly used for back up purposes?

Tape drives are a form of digital storage devices which use tape for information recording. Because of the cost effective nature of the tape material and their long archival life, tape drives are widely used for backup and archival purposes. A tape drive cannot be accessed randomly like with the hard drives to read a particular piece of data. However, the tape drives can stream data very fast once they are positioned to the particular data point. Because of this factor, tape drives cannot be used for daily storage purposes. There are many formats available for storage of digital information on tape drives. Some of the popular ones are DDS (Digital Data Storage), AIT (Advanced intelligent tape) introduced by Sony and many others. These formats have several generations. AIT is a high speed format for data storage on tapes.
The raw data capacity of tape drives is fixed. However, more amounts of data can be stored on them by using compression. Most of the tape drives have a compression ratio of 2:1. Some tape drives when used with only certain data types can achieve a compression of about 10:1 also. Tape drives can be connected to the computer by using a SCSI interface or other common types as firewire and usb. The reliability according to the recently conducted surveys is not good. Most companies do not test or try to recover from tape archives and some companies that do experienced 77 % failure in achieving a backup of stored data. So, many of the companies in 2011 are starting to move from a tape based back-up solution to a disk based solution.
A large collection of tapes in a huge structure with a mechanical tape loading device is called a tape library. Tape libraries are used for heavy data archival needs like that of financial records of a company. These data facilities take up a lot of money to setup and maintain. A tape library is a digital archive that can store huge amounts of data ranging from several TB to few PetaByte or few 1000 TBs. A trade off exists for higher storage capacities. The access time becomes slower because of mechanical parts and machines when the storage amount increases. Tape autoloaders are tape library devices with a single drive. There are several software technologies for operation of tape libraries. Some of them include open source tape library softwares like AMANDA, Bacula, and the minimal mtx program.

By: Sandeep Mahanthi

4 mm DAT tape drives and their use in back up devices:

A tape drive is relatively an older generation of storage technologies. DAT stands for Digital Audio Tape. The storage of digital data on these tapes gives rise to a computer data storage format known as DDS which means Digital Data Storage. Several versions of DDS were developed and some of these versions are still in use in the present day modern backup technology. 4 mm DAT drives and other DAT drives were used under DDS specification in a robust cockpit voice and flight data recorders as a black box for the flights, jets and aeroplanes. These are also used is several other applications where data storage with other technologies becomes unreliable.
A DDS tape drive uses helical scanning for recording the data. This is the same process that is used by VCR recorders. If any errors are found in the data stored, the write head rewrites the data. DDS generally uses a 3.8 mm wide tape drive for recording the data. However, in the newer versions of DDS, the tape width has been extended up to as much as 8 mm wide. Tape drives are sensitive to various physical conditions like dust and moisture. So, these tape drives must be cleaned regularly for efficient performance. Otherwise, the data stored might be at risk due to the physical destruction caused to the drive. Companies such as Seagate, HP and others manufacture these tape drives for back up storage purposes.
There are various generations of DDS specifications. Let us have a look at them.
DDS-1: This was the first generation of DDS and it is most commonly known as just DDS. This technology offered 1.3 GB of uncompressed data storage with a 60 meter long tape drive. When the data is compressed, the data stored can be doubled, that is 2.6 GB of compressed data. More data capacity can be achieved by using more length of tape.
DDS-2: This offered 4 GB uncompressed and 8 GB compressed data on a 120 meter long tape drive.
DDS-3: 12 GB uncompressed and 24 GB compressed data on 125 m drive. DDS 3 also uses advanced technology that minimises the electric noise and helps for cleaner data recording.
DDS-4 20 GB uncompressed and 40 GB compressed data on 150 m drive. Also known as DAT 40.
DAT 72: It was developed by HP and Certance. It offers 36 GB uncompressed with 72 GB compressed amount of data storage.
DAT 160 and DAT 320 are other generations which offered 80 GB and 160 GB of uncompressed data respectively. When compressed, double the amount of data can be stored. These latest devices have host interfaces for connecting through SCSI, USB and other standards.

By: Sandeep Mahanthi