Performance For System Z - IBM DS8800 Introduction And Planning Manual

v It might be helpful to know that some basic characteristics of Easy Tier might

Performance for System z

The DS8000 series supports the following IBM performance enhancements for
System z environments.
v Parallel access volumes (PAVs)
v Multiple allegiance
v z/OS Distributed Data Backup
v z/HPF extended distance capability
Parallel access volumes
A PAV capability represents a significant performance improvement by the storage
unit over traditional I/O processing. With PAVs, your system can access a single
volume from a single host with multiple concurrent requests.
You must configure both your storage unit and operating system to use PAVs. You
can use the logical configuration definition to define PAV-bases, PAV-aliases, and
their relationship in the storage unit hardware. This unit address relationship
creates a single logical volume, allowing concurrent I/O operations.
Static PAV associates the PAV-base address and its PAV aliases in a predefined and
fixed method. That is, the PAV-aliases of a PAV-base address remain unchanged.
Dynamic PAV, on the other hand, dynamically associates the PAV-base address and
its PAV aliases. The device number types (PAV-alias or PAV-base) must match the
unit address types as defined in the storage unit hardware.
You can further enhance PAV by adding the IBM HyperPAV feature. IBM
HyperPAV associates the volumes with either an alias address or a specified base
logical volume number. When a host system requests IBM HyperPAV processing
and the processing is enabled, aliases on the logical subsystem are placed in an
IBM HyperPAV alias access state on all logical paths with a given path group ID.
IBM HyperPAV is only supported on FICON channel paths.
PAV can improve the performance of large volumes. You get better performance
with one base and two aliases on a 3390 Model 9 than from three 3390 Model 3
volumes with no PAV support. With one base, it also reduces storage management
costs that are associated with maintaining large numbers of volumes. The alias
provides an alternate path to the base device. For example, a 3380 or a 3390 with
one alias has only one device to write to, but can use two paths.
The storage unit supports concurrent or parallel data transfer operations to or from
the same volume from the same system or system image for System z or S/390
hosts. PAV software support enables multiple users and jobs to simultaneously
access a logical volume. Read and write operations can be accessed simultaneously
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Introduction and Planning Guide
limit the applicability for your generalized workloads. The granularity of the
extent that can be relocated within the hierarchy is large (1 GB). Additionally,
the time period over which the monitoring is analyzed is continuous, and long
(24 hours). Therefore, some workloads may have hot spots, but when considered
over the range of the relocation size, they will not appear, on average, to be hot.
Also, some workloads may have hot spots for short periods of time, but when
considered over the duration of Easy Tier's analysis window, the hot spots will
not appear, on average, to be hot.