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Friday, August 15, 2008

The DAT-DDS Tape Technology

The Digital Audio Tape DAT technology is the most prolific of all tape technologies. The DAT tape was previously known as DDS Digital Data Storage. Over 15 million DAT drives have been shipped since the first products were introduced in 1989 and more than 6 million since 2000. This gives rise to a conservative estimate of a 6-million user installed base. The HP StorageWorks DAT160 tape drive is the latest edition to the DAT family. It was launched by HP in June 2007. The DAT-160 drive is an evolution of existing DAT technology and has much in common with the previous five generations of DAT. It is estimated that there are over 6 million DAT tape drives currently installed worldwide. The DAT media tape cartridge is the Low-cost media and provides its customers the lowest cost of ownership.

The HP StorageWorks DAT 160 tape has 80-GB native capacity and up to 160 GB with 2:1 data compression. The HP DAT-160 has a transfer rate of 6.9 MB/sec native, over 13.8 MB/sec with 2:1 data compression. The DAT160 provides approximately 160 GB backing up in under 4 hours. Higher capacity can be achieved mainly by using wider tape for DAT160, but still provides backward write and read compatibility with DAT72 and DAT40 media. This can be done by having two independent threading mechanisms and tape paths inside the device.

DAT 160 supports HP StorageWorks One Button Disaster Recovery Solution when used with the relevant software and HP ProLiant servers, allowing total rebuild of a server from a single backup tape. It also includes Single Server Edition of HP Data Protector Express backup/recovery and disaster recovery software. DAT-160 media cartridge is supported on a wide range of operating system and backup applications.

Enterprise backup compatibility (EBS)

  • Enterprise (E-Series) libraries
  • Virtual (VLS) libraries
  • Business (MSL) libraries
  • 1/8 G2 tape autoloaders
  • 1/8 tape autoloaders
Tape Backup compatibility
  • DAT/DDS tape drives
  • DAT/DDS tape autoloaders
  • DLT/SDLT tape drives
  • LTO Ultrium tape drives & blades
  • DVD RW optical drives
The DAT160 media is just a wider version of the DAT40 media using MP Metal Particle technology 150 m in length. This is the same type of tape as has been shipping since 1994 in DAT40 cartridges. It has a proven track record of reliability. However, in DAT160 media, wider version of the tape has been used to enable greater capacity. A DAT160 drive accepts both sizes of media but threads them around the drum in different ways.

Transfer rate on DAT technology is determined partly by the wrap angle (amount of tape wrapped around the rotating helical scan drum) and the speed of rotation of the drum. The wrap angle of the DAT160 drive is 180 degrees compared to only 90 degrees for previous generation DAT technologies, so the DAT-160 drive actually makes more efficient use of tape in contact with the head to increase transfer rate. Further generations will increase the drum speed.

The HP approach of using independent tape threading mechanisms was the breakthrough that enabled the DAT160 drive to write and read DAT-72 and DAT-40 media. When the concept of loading two different heights of cartridge with two different tape widths was invented, HP used extensive computer simulation techniques to model the tape threading and routing for each tape type. The results of these simulations indicated that the design concepts were both practical and yielded good levels of margin in allowing the design to be successful.

The most difficult challenge has been accommodating all the mechanical components in the physical space available. However, using the HP standard product design and testing methodology, the necessary mechanical solutions and enhancements have been evolved. The robust engineering and margin in these tape guides are the keys of a successful interchange.

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