If a Logical Volume Manager (LVM) is used, BRBACKUP can only save all files from a hard disk to tape if the logical volumes are not unnecessarily distributed over several hard disks (see configuration A).

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 (for example 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. Configuration B, however, can provide a better performance for online operation of the SAP system.

If you plan the configuration of logical volumes for large databases, you should find a compromise for the options which meets your requirements. You should consider which is more important: a more effective backup or higher performance of the online operation of the SAP system.

Some notes on this point:

• 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 possible (configuration B) deterioration of optimization through BRBACKUP

• Although the higher security and availability of your datasets provided by using the LVM has a generally high priority, you should consider whether you could do without an LVM. You lose the above-mentioned advantages this way, but, on the other hand, you can carry out a backup of the datasets considerably more effectively by means of BRBACKUP.

• In large databases, the configuration of the database files is not variably selectable. Every change to the configuration (for example, structure changes due to a tablespace extension or a tablespace reorganization with data files) must always be planned with respect to the physical hard disk configuration and the influence that this will have on the performance. The use of an LVM therefore has no major advantage in this case.