IBM TotalStorage DS6000 Series: Performance Monitoring and Tuning

Chapter 4. Planning and monitoring tools 137

IBM TotalStorage Productivity Center for Disk report and zSeries

The z/OS systems have proven performance monitoring and management tools available to

use for performance analysis. RMF, a z/OS performance tool, collects performance data and

reports it for the desired interval. It also provides cache reports. The cache reports are similar

to the Disk-to-Cache and Cache-to-Disk reports available in the TotalStorage productivity

Center for Disk, except that RMF’s cache reports are provided in text format. The RMF

provides the Rank level statistics as SMF records. These SMF records are raw data that you

can run your own post processor against to generate reports. RMF is discussed in detail in

Chapter 10, “zSeries servers” on page 357.

4.3.9 IBM TotalStorage Productivity Center for Disk in mixed environment

A benefit of the IBM TotalStorage productivity Center for Disk is that you can analyze both

open systems fixed block (FB) and S/390 CKD workloads. When the DS6000 subsystems are

attached to multiple hosts running on different platforms, open systems hosts may affect your

S/390 workload and vice versa. If this is the case, taking a look at RMF reports will not be

sufficient. You need also the information about the open systems. The IBM TotalStorage

Productivity Center for Disk informs you about the cache and I/O activity.

Before beginning the diagnostic process, you must understand your workload and your

physical configuration. You need to know how your system resources are allocated, as well as

understand your path and channel configuration for all attached servers.

Let us assume that you have an environment with a DS6000 attached to a z/OS host, an AIX

pSeries host, and several Windows hosts. You have noticed that your z/OS online users

experience a performance degradation between 7:30 a.m. and 8:00 a.m. each morning.

You may notice that there are 3390 volumes indicating high

disconnect times, or high device

busy delay

time for several volumes in the RMF device activity reports. Unlike UNIX or

Windows, you may notice

response time and its breakdown to connect, disconnect, pending,

and IOS

queuing.

Disconnect time is an indication of cache miss activity or destage wait (due to persistent

memory high utilization) for logical disks behind the DS6000s.

Device busy delay is an indication that another system locks up a volume, and an extent

conflict

occurs among S/390 hosts or applications in the same host when using Parallel

Access Volumes. The DS6000’s multiple allegiance or Parallel Access Volume capability

allows it to process multiple I/Os against the same volume at the same time. However, if a

read or write request against an extent is pending while another I/O is writing to the extent, or

if a write request against an extent is pending while another I/O is reading or writing data from

the extent, the DS6000 will delay the I/O by queuing. This condition is referred to as

extent

conflict.

Queuing time due to extent conflict is accumulated to device busy (DB) delay time.

An extent is a sphere of access; the unit of increment is a track; usually I/O drivers or system

routines decide and declare the sphere.

To determine the possible cause of high

disconnect times, you should check the read cache

hit ratios, read-to-write ratios, and bypass I/Os for those volumes. If you see the cache hit

ratio is lower than usual while you have not added other workload on your S/390 environment,

I/Os against open systems fixed block volumes might be a cause of the problem. Possibly

fixed block (FB) volumes defined on the same server had a cache-unfriendly workload, thus

impacting your S/390 volumes hit ratio.

In order to get more information about cache usage, you can check the cache statistics of the

Fixed Block volumes, which belong to the same server. You may be able to point out the Fixed

Block volumes that have a low read hit ratio and short cache holding time. If you can move the