IBM DS8880 Series, Introduction And Planning Manual

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Performance for IBM Z
The storage system supports the following IBM performance enhancements for
IBM Z environments.
v Parallel Access Volumes (PAVs)
v Multiple allegiance
v z/OS Distributed Data Backup
v z/HPF extended distance capability
v zHyperLink
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 specific 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 IBM 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
to different domains. (The domain of an I/O operation is the specified extents to
which the I/O operation applies.)
Multiple allegiance
With multiple allegiance, the storage unit can run concurrent, multiple requests
from multiple hosts.
Traditionally, IBM storage subsystems allow only one channel program to be active
to a disk volume at a time. This means that, after the subsystem accepts an I/O
request for a particular unit address, this unit address appears "busy" to
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DS8880 Introduction and Planning Guide