Database Reference
In-Depth Information
separation is application specific; some use tape marks to designate the end of
a file, and others use them to separate blocks of a file. Tape mark processing is
expensive and defeats the drive's ability to stream data. Enterprise tape drives
include features to quickly seek to a particular place on the tape by avoiding
the use of tape marks. One enterprise tape drive utilizes a special track on the
tape called the servo track and a special index at the beginning of the tape to
quickly position the tape to a particular point. The slowest tape seek times oc-
cur when applications move down the length of the tape counting tape marks
to locate the data. Some applications, such as the high-performance storage
system (HPSS) software, are careful to allow placement of small files on tape
with better access speed and larger files on slower access, high-capacity tape.
In terms of durability, tape is at least as durable as other data storage
technologies. Depending on the amount of reuse, format and density of the
tape, and the speed and handling of the drive, tape can be used for several
decades to store data.
1.4.2 Enterprise-Class Tape Technology
Enterprise tape drives are designed and manufactured under the strictest spec-
ifications to ensure extra reliability and durability of user data. Features in-
clude redundant components internal to the tape drives to eliminate any single
point of failure to the greatest extent possible. At least one tape drive avail-
able in the market has dual tape heads, the most expensive component of
the drive, to ensure that tape head failure does not interrupt tape drive data
transfer capabilities.
Enterprise-class drives provide ruggedized components to handle extra wear
and tear they receive from high utilization. Tape media wear is also a primary
consideration in designing enterprise quality tape drives. Enterprise-class tape
drives are typically capable of adjusting tolerances, such as tension on the tape
or recording head positions, and are an order of magnitude more accurate than
commodity tape drives.
Another consideration in differentiating between enterprise and commodity
tape drives is the bit error rate capabilities of the drive. Commodity tape
drives have bit error rate on the order of 10E-17. Currently, enterprise tape
drive manufacturers are able to design the recording head and the pattern of
data written to media to reduce bit error rate by up to two orders of magnitude
compared with commodity tape drives. One other feature that enterprise class
drives provide are multiple control and data path connections to the drive.
The main purpose of tape libraries is to provide storage for tape cartridges
not in use and to load or unload tapes in or out of tape drives to the tape
library. Enterprise class tape libraries provide redundant components such as
robotic arms, grippers, visioning systems, and power feeds to prevent a single
point of failure. When failures occur, hot swappable capabilities (such as re-
placing robotics while the library remains available for use) become another
