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Chapter 5. Virtualization concepts 95
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.
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.
LSS X'17'
DB2
LSS X'18'
DB2-test
Physical Drives Logical Volumes