Technical specification for DLT tape backup and drives!

Every IT based business environment handling mission critical applications give importance to the data integrity of electronic data on storage media. Such enterprise management insists on stable and durable products as a way to minimize the frequency and level of data storage computer errors.

The advantage of DLT tape backup is largely based on its verified durability combined with its high storage capacity and high data transfer rates. The DLT’s technical hardiness is based on the fact that the tape media inside the cartridge does not actually touch the head in the drive.

The transport mechanism is designed in such ways that instead of gripping the tape from the middle and pulling it in to place, the DLT tape storage drive assembly grabs one end of the tape, pulling it out of the cartridge, and gently wraps it around the take-up reel in the drive. The wrap angles around the rollers are gentle which result in less tension being placed on the head and the tape.

A lower abrasivity that is achieved by the head guide assembly of the drive minimizes the physical friction on the drive heads. This leads to a longer drive and head life which makes the maintenance cost lower. Tests results specify the DLT drive’s head life as 30,000 hours compared to 2,000 hours for the 8mm helical scan DAT technologies. The DLT cartridge has tape life of 500,000 head passes, which is significantly higher than any other tape storage media.

DLT backup tapes provide Higher Storage Capacity.
DLT cartridges use a system with 0.5 inch wide metal particles tape housed in a 5.25 inch Full Height form factor single reel cartridge. Very high recording density data storage is achieved by recording the data in a serpentine pattern on numerous tracks (grouped in pairs) that are laid parallel to one another and spanning the entire length of the tape. At the time of recording, the first set of track is recorded on the entire length of the tape. Once the tape end is reached, the heads is automatic vertically stepped up allowing it to record a new set of tracks along the tape, this time in opposite direction. The process is repeated, back and forth until the tape is full, allowing data to be recorded as a series of linear strips.

Table below depicts the primary characteristics of known DLT formats to date:

DLT 2000  DLT 4000  DLT 7000  DLT 8000  Capacity  15 GB  20 GB  30 GB  40 GB  Maximum Transfer Rate  1.25 MB/s  1.5 MB/s  5 MB/s  6 MB/s

DLT ‘s Error Correction Code (ECC) provides maximum data protection.
DLT tape storage units incorporate multi-layer data integrity methodology to maximize error detection as a way to accomplish complete subsystem data protection. At the heart of DLT’s error detection capabilities is CRC-64 error detection code. To complement it, other alternative error strategy detection methods like EDC-16, CRC-16 are used as a way to provide undetected error rate of 1/1027 – This means that an error will go undetected only ones out of 1027 cases.
The 20 blocks long data segment of DLT tape is defined as – 16 blocks of user data and 4 blocks of ECC (containing CRC, EDC, indexes and control field).

So during read operation the DLT drives can effectively recover up to four consecutive 4KB blocks of data within a 20-block entity. In case the error spans more than 4 blocks of data in a 20-block entity, the DLT adaptively retry algorithm rereads the entity multiple times in an effort to recover the data.

Conclusion:
With a single tape native capacity of 40GB in conjunction with sustained transfer speeds of up to 6MB/sec the DLT tape data backup technology as one tape technology is the perfect information solution for storage and for archiving needs of network servers, mid-range systems and high-end workstations.