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Compaq DAT AutoLoader Reference Guide
Compaq Confidential – Need to Know Required
Writer: Debbie McRill Project: Compaq DAT AutoLoader Reference Guide Comments:
Part Number: 326817-003 File Name: b-ch1 Overview.doc Last Saved On: 1/25/00 9:55 AM
Projected Duty Cycle
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.
Capacity
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.
Table 1-1
Tape Drive Capacity
Compaq Tape AutoLoader Computer Capacity
2/4 GB DAT 2-4 GB or less
4/8 GB DAT 4-8 GB or less
12/24 GB DAT 12-24 GB or less
20/40 GB DAT 20-40 GB or less
Data Compression
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.