IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

76 IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

To create the DS6000 logical volume, also known as a Logical Unit or LUN, extents from the

selected Extent Pool are concatenated to allocate the required LUN capacity. If an Extent

Pool is made up of several Ranks, a LUN can potentially have extents on different Ranks and

so be spread over those Ranks.

However, to be able to create very large logical volumes, you must consider having Extent

Pools that span more than one Rank.

Combining Extent Pools made up from one Rank and then utilizing an open systems

host-based Logical Volume Manager (LVM) to stripe a host Logical Volume over LUNs

created on each Extent Pool, will offer a balanced method to evenly spread open systems

data across the DS6000.

The logical volume stripe size

Each striped logical volume that is created by the open system host’s logical volume manager

has an optional stripe size that specifies the fixed amount of data stored on each DS6000

logical volume (LUN) at one time.

3.7 .Performance and sizing considerations for z/OS

Here we discuss some z/OS-specific topics regarding the performance potential of the

DS6000. We also address what to consider when you configure and size a DS6000 to replace

older storage hardware in z/OS environments.

3.7.1 Performance potential in z/OS environments

The DS6000 can be configured with 8 host Fibre attachment ports, which may be individually

configured to operate with FICON or Fibre Channel protocols. Four of these ports are

preferentially managed by server0 within the DS6000 and the other four host ports are

managed by server1. As with the open systems attachment, we strongly recommend that

zSeries hosts are connected in a balanced manner across both the DS6000 servers.

Note: We recommend assigning one Rank per Extent Pool to control the placement of the

data. When creating a logical volume in an Extent Pool made up of several Ranks, the

Extents for this logical volume should be taken from the same Rank if possible. This

implies that you have no logical volumes that span Ranks, and can be done carefully with

the DSCLI. It is much more difficult to micromanage LUN placement while using the DS

GUI.

Note: z/OS does not provide any LVM functionality, and supports CKD volumes up to a

maximum size of 64 KB (actually 64 KB (65536) bytes less 256, or 65280 bytes).

Note: The logical volume stripe size has to be large enough to keep sequential data

relatively close together, but not too large so as to keep the data located on a single Array.

The recommended stripe sizes that should be defined using your host’s logical volume

manager are in the range of 4 MB to 64 MB.

You should choose a stripe size close to 4 MB, if you have a large number of applications

sharing the Arrays, and a larger size, when you have very few host servers or applications

sharing the Arrays.