This section describes how a Logical Volume Manager (LVM) influences the optimization of file distribution during an Oracle database backup.
These consideration do not apply to large disk arrays, where the whole database is stored in one array.
If you use an LVM, BRBACKUP can only save all files from a hard disk to tape if the logical volumes are not scattered over several hard disks. Configuration A of the graphic below is better suited for backup with an LVM.
Each logical volume exactly corresponds to one hard disk. For example logical volume 1 = disk 1, logical volume 2 = disk 2, logical volume 3 = disk 3.
Each logical volume is set up so that it covers areas of all the hard disks:
· Logical volume 1 = area1.disk1 + area1.disk2 + area1.disk3
· Logical volume 2 = area2.disk1 + area2.disk2 + area2.disk3
· Logical volume 3 = area3.disk1 + area3.disk2 + area3.disk3
Configuration A is more efficient than configuration B with respect to database backup. However, configuration B can provide better performance for online operation of the SAP system.
When planning the configuration of logical volumes for large databases, you need to find a compromise between the following:
· More effective backup
· Higher SAP System performance
Consider the following factors:
· Advantages of using an LVM
Easier administration, high flexibility, higher security by using RAID systems
· Disadvantages of using an LVM
Performance loss through management overhead and possibly – in configuration B – reduced optimization with BRBACKUP
· Although the higher security and availability of your datasets provided by using the LVM has a generally high priority, consider whether you could do without an LVM:
Ў You lose the LVM advantages outlined above.
Ў However, you can perform a dataset backup much more effectively using BRBACKUP.
· In large databases, the configuration of the database files is not variably selectable. You must consider the effect on physical disk configuration and the influence this has on performance when you make changes to the configuration, such as structure changes due to a tablespace extension or a tablespace reorganization.