6-6
Preventative Maintenance
500300 Rev. U
6.5.3
Media Requirements
The drive operates reliably using any tape meeting the requirements of ANSI X3.40-
1983 and certified for 6250 CPI. Defective tapes and tapes that have been damaged
or subjected to heavy wear may not load or pack properly and should not be used.
Tapes frequently wear out near the beginning of tape (BOT) tab as this is the area of
greatest use. Tapes that are worn near the beginning can receive new life by cutting
off the first 25 to 50 feet and affixing a new BOT reflective tab. This tab must be
located 16 ±2 feet from the beginning of the tape and positioned on the outside
surface of the tape at the edge nearest the tape reel label. The drive supports 6
through 10.5-inch reel sizes, and both 1.5 and 1.0 mil tape.
6.6
Data Capacity
The total data capacity of a tape is determined by the following factors:
1.
Tape Length
- Tape length is defined as the distance between the BOT and
end of tape (EOT) reflective tabs. The data capacity is directly proportional to
the tape length.
2.
Recorded Density
- The drive provides recording densities of 1600, 3200 and
6250 CPI. If data were written in one continuous block from BOT to EOT, a
tape could hold twice as much data at 3200 CPI than at 1600 CPI.
3.
IBG Length
- Data is not normally written in one continuous stream, but in a
series of individual blocks, each separated by an IBG. The length of the IBG is
0.6-inch in the NRZI, PE and DPE modes, and 0.3-inch in the GCR mode.
Because the IBG is an erased area of tape, the total data capacity of a given
tape is reduced by the total accumulative length of the IBGs.
4.
Block Length
- Because every block is followed by an IBG, the number of data
characters per block greatly affects the amount of data that will fit on any
specified tape length. As the block length is increased for a given length of
tape, the number of IBGs in that length will decrease, and the data capacity
will increase.
In addition to the IBG, each data block recorded in the GCR, DPE and PE
modes contains several non-data characters. The non-data characters are
necessary to properly decode the data and to provide a means of on-the-fly
error correction. They add to the overall block length and decrease tape
capacity accordingly.
5.
Filemarks
- A filemark is a uniquely recorded mark on the tape that the
system can use to group blocks together into a file. In addition to the standard
IBG, each filemark is preceded by a filemark gap. The filemark gap is 3.5-
inches of erased tape (an option in the Drive Configuration menu reduces the
filemark gap to 0-inch). As the number of filemarks on a given length of tape
increases, the data capacity for that length decreases.
