Oracle Secure Backup 10.3, Руководство по установке и настройке, Страница: 17 / 174

Oracle Secure Backup Concepts
Introduction to Oracle Secure Backup 1-7
When Oracle Secure Backup begins a restore operation, it does not know what block
size was used to write a given tape. Because issuing a read for a too-small block would
result in an error condition and a tape reposition, Oracle Secure Backup always starts a
restore operation by reading the largest possible block size. This is either the current
setting of the
media/maxblockingfactor
policy or the tape drive configuration
attribute. The maximum blocking factor, therefore, must always be greater than or
equal to the largest block size you ever want to restore.
After the first read from the backup image, Oracle Secure Backup compares the
amount of data requested to the actual size of the block and adjusts the size of
subsequent reads to match what is on the tape.
Each tape drive supports a specific tape format. Typical tape formats include:
■
8mm
■
4mm, or Digital Audio Tape (DAT)
■
Advanced Intelligent Tape (AIT)
■
Digital Data Storage (DDS)
■
Digital Linear Tape (DLT) and Super DLT (SDLT)
■
Linear Tape-Open (LTO), an open alternative to the proprietary DLT format
Information about the tape formats of tape devices supported by Oracle Secure
Backup is available at the following URL:
http://www.oracle.com/technology/products/secure-backup
Tape Libraries
A tape library is a robotic tape device that accepts SCSI commands to move a volume
between a
storage element and a tape drive. A tape library is often referred to as a
robotic tape device, autochanger, or medium changer.
A tape library contains one or more tape drives, slots to hold tape cartridges, and an
automated method for loading tapes.
Figure 1–3 illustrates a tape library that contains
four tape drives.