Projected Duty Cycle; Capacity; Data Compression - Compaq DAT AutoLoader Reference Manual

1-4 Compaq DAT AutoLoader Reference Guide

Projected Duty Cycle

Capacity

Data Compression

The projected duty cycle of the Compaq 20/40 GB DAT 8-Cassette
AutoLoader is an important consideration in determining the amount of time
required for backup of a given system, as well as how often it is necessary to
clean the tape drive's read/write heads.
For example, a nightly, unattended complete 18-GB backup is well within the
capacity of one 20/40 GB DAT drive. However, at a backup rate of
approximately 8GB/hour, that tape drive is in operation for approximately 2
1/4 hours every night of the week. With this amount of usage, the tape drive's
read/write heads should be cleaned every 4 to 6 weeks. If the drive heads are
not cleaned soft errors and overall backup time increases and eventually
causes the drive to fail.
The best method for building hardware reliability into a backup strategy is to
ensure that the backup hardware is matched to the computers. Table 1-1 relates
various computers with the appropriate tape drives. If you need special, partial
backups in addition to the routine backups, select the next larger drive size.
Compaq Tape AutoLoader
2/4 GB DAT
4/8 GB DAT
12/24 GB DAT
20/40 GB DAT
The Compaq 20/40 GB DAT 8-Cassette AutoLoader ships from the factory
with data compression enabled for writing. The drive is equipped with onboard
DDS-DC hardware, using the Data Compression Lempel Ziv (DCLZ)
algorithm. In this mode, data is always compressed when writing to the
cassette, but the drive is capable of reading both compressed and
uncompressed cassettes.
Table 1-1
Tape Drive Capacity
Computer Capacity
2-4 GB or less
4-8 GB or less
12-24 GB or less
20-40 GB or less