Ibm ZVSE PARALLEL ACCESS User Manual
z/VSE Parallel Access Volume White Paper 12/08/2009
z/VSE Parallel Access Volume Support
Vischer, Andreas
z/VSE I/O Lead Developer
vischer@de.ibm.com
IBM Germany Research & Development GmbH
Schoenaicherstr. 220
71032 Boeblingen
Germany
IBM Germany Development & Research GmbH
©Andreas Vischer
z/VSE Parallel Access Volume White Paper 12/08/2009
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IBM Germany Development & Research GmbH
©Andreas Vischer
z/VSE Parallel Access Volume White Paper 12/08/2009
Base Volume
Base Volume
I/O
I/O
I/O
I/O
Alias
Alias
I/O I/O
Overview
Parallel access volumes (PAV) allow your system to access volumes in parallel when you use an IBM
System z host.
PAV is a feature of IBM System Storage Disk Systems which enables more than one I/O operation to be
processed for a single logical device. The use of PAVs can significantly reduce device queue delays to busy
devices (all I/O operations are normally processed from a single queue). PAVs are managed by creating
multiple addresses for a single logical device.
PAV is an optional licensed feature of the IBM System Storage DS8000 and DS6000 series, available with
the PAV indicator feature, and corresponding DS8000/DS6000 series function authorization. PAV also
requires the purchase of the FICON/ESCON Attachment feature in the Turbo models.
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.
PAV can improve the performance of large volumes. You can 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.
The storage unit supports concurrent or parallel data transfer operations to or from the same volume from
the same system or system image on System z hosts. A System z with 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.)
Today, a PAV volume has one volume serial number and multiple subchannels.
When accessing a PAV volume in parallel, reads can be processed simultaneously from the subchannel
point of view, as well as writes to different areas on the volume.
z/VSE will balance I/O traffic upon the available base and alias volumes by an internal algorithm and
considers of course load balancing.
IBM Germany Development & Research GmbH
©Andreas Vischer
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