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IBM-AUSTRIA - PC-HW-Support 30 Aug 1999 |
Media Reliability
Media Reliability
A second factor in overall reliability is media
reliability. Again, published figures tend to get confusing and are hard
to compare.
The following terminology is commonly used:
| Error Rate |
Average number of errors that can be expected per one unit of |
information processed, and this on the entire population of tapes.
| Reliability |
Number of units processed per one error, or the inverse of the error rate. |
When looking at these figures, ask yourself
the following questions before actually comparing them:
- Are these calculated or measured values?
- If calculated, what are the underlying assumptions?
- If measured, is it the average over the entire population?
- Who performed the tests or calculations?
- What do they mean by an error?
Most bit or byte
level errors could go undetected, because an ECC mechanism in tapes can
correct them. An error that would fail the system would probably be an
error on an entire block of data.
Another published figure in media
reliability is life expectancies. The problem however is that this value
is highly dependent on external factors, like temperature and humidity.
As a general rule, DLT and Travan technologies have a better reliability
than 4 or 8 millimeter tapes.
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