Storix Software SBAdmin User Guide - Manual (Page 47)

By default, the Physical Device Type field will be set to “Tape/Library”. If you want to create a directory-based
device for writing backups to disk on the server, select “Disk/Directory” instead. The remaining options will differ
depending on the device type you are configuring:
Tape Devices
The physical tape drives available on the server will be shown in the listbox. Most often a single tape drive is
used independently. In this case, just select a single tape drive from the list.
Tape Write Policy
When using a single tape drive that is not a part of an autoloader or tape library, only the Sequential write
policy is used. The write policies are defined as follows:
•
Sequential - This device may contain one or more tape drives. If multiple drives are used, the backup
will start on the first drive and automatically continue on the next drive when the first tape is full. The
user is prompted to change tapes only when the tape in the last drive is full. Backups created to a
sequential device may be restored using any single drive, provided all drives used to create the backup
were of the same type.
A single drive may also be configured as a sequential device. However, there would only be an
advantage if you are using a
sequential autoloader or random library . If so, the device will eject the
tape when it becomes full, and the autoloader or random library will automatically change the tape,
allowing the backup to continue unattended.
•
Parallel - This device must consist of two or more tape drives. The data in the backup will be evenly
spread, or striped, across all of the tape drives, allowing the backup to complete in a fraction of the
time it would take to write to a single drive. The same parallel device (or one containing the same
number and types of drives) must be used to restore data from the backup.
•
Multi-copy - This device must consist of two or more tape drives. When backups are sent to this device,
the same data is written to all drives, providing multiple copies of the same backup in about the same
time it would normally take to make a single copy to a single drive. Any copy of the backup may be
read from any single tape drive.
When reading data from a backup made with a multi-drive device, it is necessary that the tapes be placed
in the corresponding tape drives in the same fashion as they were during the backup. This does not apply
to a multi-copy device backup since each set of tapes from a single drive are independent copies of the
same backup, and may only be read by a single device or a sequential device (you can still use a multi-
copy device to perform the restore, but only the first drive is read).
The following illustrations show how the data is saved on each of the different multi-drive devices. Note
how the tape volumes are numbered for each write policy when data spans a different physical tape.
Storix System Backup Administrator 47 Version 8.2 User Guide