1-4Compaq DAT AutoLoader Reference Guide
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.
