Load Time
Load time is the time from the moment you insert a cartridge into
the drive, until the cartridge is ready to read or write the data.
When discussing the DLTtape system, competitors often make the
accurate statement that the load time spec for a DLTtape cartridge
is approximately one minute. While accurate, that statement is not
complete. Load time for a DLTtape cartridge is approximately one
minute, but only for the first time a blank cartridge is loaded. After
that, it usually takes 35 to 45 seconds for the tape to load. The dif-
ference is due to the fact that, on the first load, the drive runs cali-
bration tests and writes initial calibration information on the tape.
On successive loads of the cartridge, the drive need only read the
previously-recorded calibration information.
Compression Algorithms
One last compression related issue: how is compression accom-
plished? In most cases, compression is done by the tape drive itself.
Several different compression technologies are used. Quantum
DLTtape systems use the LZ (Lempel Ziv) compression algorithm.
This algorithm has advantages over other algorithms, in terms of
effectiveness across most types of data. In our experience, we have
frequently achieved compression ratios of 4:1, and have had specif-
ic instances as high as 25:1. However, for the DLTtape system,
Quantum continues to be conservative and uses the industry stan-
dard 2:1 figure when using compression data figures.
Reliability/MTBF
If your tape drive is subject to heavy usage, running eight or ten
hours a day, or if it runs all night doing backups, then reliability is
important, and MTBF is one way to determine reliability. MTBF is
the most commonly used reliability spec. It specifies the most likely
interval of time that will go by before the unit will fail. With some
exceptions, this refers to a failure of any part of the unit, for any cause,
under normal usage. A figure of 10,000 hours means that the manufac-
DEMYSTIFYING TAPE DRIVE SPECS
6.4
