IBM DS8000 manual Placement of data, Virtualization hierarchy

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 effort.

Figure 5-12summarizes the virtualization hierarchy.

Array	RAID
Site	Array
	Data
	Data
	Data
	Data
	Data
	Data
	Parity
	Spare

Rank

Type FB

1 GB FB 1 GB FB 1 GB FB

Server0

	Extent	Logical
	Pool	Volume
1 GB FB	1 GB FB	1 GB FB
1 GB FB	1 GB FB	1 GB FB

LSS	Address	Volume	Host
FB	Group	Group	Attachment

X'2x' FB

4096

addresses

LSS X'27'

X'3x' CKD

4096

addresses

Figure 5-12 Virtualization hierarchy

5.3.9 Placement of data

As explained in the previous chapters, there are several options on how to create logical volumes. You can select an extent pool that is owned by one server. There could be just one extent pool per server or you could have several. The ranks of extent pools could come from arrays on different device adapter pairs and different loops or from the same loop. Figure 5-13 on page 100 shows an optimal distribution of eight logical volumes within a DS8000. Of course you could have more extent pools and ranks, but when you want to distribute your data for optimal performance, you should make sure that you spread it across the two servers, across different device adapter pairs, across the loops, and across several ranks.

If you use some kind of a logical volume manager (like LVM on AIX) on your host, you can create a host logical volume from several DS8000 logical volumes (LUNs). You can select LUNs from different DS8000 servers, device adapter pairs, and loops as shown in Figure 5-13.By striping your host logical volume across the LUNs, you will get the best performance for this LVM volume.

Chapter 5. Virtualization concepts 99