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Chapter 4. Virtualization concepts 79
Figure 4-10 Host attachments and volume groups
Figure 4-10 shows the relationships between host attachments and volume groups. Host
AIXprod1 has two HBAs, that are grouped together in one host attachment and both are
granted access to volume group DB2-1. Most of the volumes in volume group DB2-1 are also
in volume group DB2-2, accessed by server AIXprod2. In our example there is, however, one
volume in each group that is not shared. The server in the lower left has four HBAs and they
are divided into two distinct host attachments. One can access some volumes shared with
AIXprod1 and AIXprod2, the other HBAs have access to a volume group called docs.
4.2.9 Summary of the virtualization hierarchy
Going through the virtualization hierarchy we started with just a bunch of disks that were
grouped in array sites. An array site was transformed into an array, eventually with spare
disks. The array was further transformed into a rank with extents formatted for FB or CKD
data. Next, the extents were added to an extent pool which determined which storage server
would serve the ranks and aggregated the extents of all ranks in the extent pool for
subsequent allocation to one or more logical volumes.
Next we created logical volumes within the extent pools, assigning them a logical volume
number that determined which logical subsystem they would be associated with and which
server would manage them. Then the LUNs could be assigned to one or more volume
groups. Finally, the host HBAs were configured into a host attachment that is associated with
a given volume group.
This new virtualization concept provides for much more flexibility. Logical volumes can
dynamically be created and deleted. They can be grouped logically to simplify storage
management. Large LUNs and CKD volumes reduce the total number of volumes and this
also contributes to a reduction of the management efforts.
Figure 4-11 on page 80 summarizes the virtualization hierarchy.
WWPN-1 WWPN-2
Host attachment: AIXprod1
Volume group: DB2-1
WWPN-3 WWPN-4
Host attachment: AIXprod2
Volume group: docs
WWPN-5 WWPN-6
WWPN-7
WWPN-8
Host att: Test
Host att: Prog
Volume group: DB2-2
Volume group: DB2-test