IBM DS8000 manual DB2

created and determines the LSS that it is associated with. The 256 possible logical volumes associated with an LSS are mapped to the 256 possible device addresses on an LCU (logical volume X'abcd' maps to device address X'cd' on LCU X'ab'). When creating CKD logical volumes and assigning their logical volume numbers, users should consider whether Parallel Access Volumes (PAV) are required on the LCU and reserve some of the addresses on the LCU for alias addresses. For more information on PAV see Chapter 10, “The DS Storage Manager - logical configuration” on page 189.

For open systems, LSSs do not play an important role except in determining which server the LUN is managed by (and which extent pools it must be allocated in) and in certain aspects related to Metro Mirror, Global Mirror, or any of the other remote copy implementations.

Some management actions in Metro Mirror, Global Mirror, or Global Copy operate at the LSS level. For example the freezing of pairs to preserve data consistency across all pairs, in case you have a problem with one of the pairs, is done at the LSS level. With the option now to put all or most of the volumes of a certain application in just one LSS, this makes the management of remote copy operations easier (see Figure 5-9). Of course you could have put all volumes for one application in one LSS on an ESS, too, but then all volumes of that application would also be in one or a few arrays, and from a performance standpoint this was not desirable. Now on the DS8000 you can group your volumes in one or a few LSSs but still have the volumes in many arrays or ranks.

Physical Drives	Logical Volumes
	LSS X'17'
	DB2
	LSS X'18'
	DB2-test

Figure 5-9 Grouping of volumes in LSSs

Fixed block LSSs are created automatically when the first fixed block logical volume on the LSS is created and deleted automatically when the last fixed block logical volume on the LSS is deleted. CKD LSSs require user parameters to be specified and must be created before the first CKD logical volume can be created on the LSS; they must be deleted manually after the last CKD logical volume on the LSS is deleted.

Chapter 5. Virtualization concepts 95