STORE and TurboSTORE/iX Products Manual (B5151-90003)

48 Chapter3
Preparing Storage Devices
Preparing Tape and DDS Devices
Multiple devices can be used as:
• Sequential devices.
• Parallel devices.
• Parallel device pools.
Using Tape Devices Sequentially
With sequential backup devices, when the first backup on the first backup device is filled,
it immediately begins writing files to a second backup on the second backup device and the
first backup rewinds. When the first backup is rewound, you can unload it and prepare the
drive with a new backup. You do not lose time while the first backup is rewinding nor while
you are loading a new backup.
When the backup on the last sequential device is filled, the process returns to the first
device. It continues cycling through all the devices in the device pool until all of the
specified files are stored.
The maximum number of serial magnetic tape or DDS devices allowed is 8. However, you
generally do not need to use more than two devices in serial. You get better backup
performance if you use multiple devices in parallel. However, using two devices in serial
can be useful for some unattended backup functions. For example, if your backup usually
fits on one media, then using two devices in serial allows your backup to finish unattended,
even if your data grows and one night overflows one piece of media.
Serial devices can also help a backup to continue unattended in the event of a media write
error. If STORE encounters an error writing to a backup media, it marks the current media
bad and unloads it. It then rewrites the backup data to the next mounted serial device, and
the backup continues uninterrupted. This gives you enough time to mount another media
on the other drive, if needed.
Figure 3-8. illustrates a sequential device backup.
Figure 3-8. Sequential Backup