IBM ZVSE PARALLEL ACCESS Manuale utente

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

z/VSE Parallel Access Volume Support

Vischer, Andreas

z/VSE I/O Lead Developer

[email protected]

IBM ermany Research & Development mbH

Schoenaicherstr. 220

71032 Boeblingen

ermany

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

Trademarks

The following are trademarks of the International Business Machines Corporation in the United States and/or other

countries. For a complete list of IBM Trademarks, see

www.ibm.com/legal/copytrade.shtml: e-business logo, eServer, FICON, IBM, IBM Logo, VSE/ESA, z/VSE,

System z

* All other products may be trademarks or registered trademarks of their respective companies.

NOTES:

All statements regarding IBM's future direction and intent are subject to change or withdrawal without notice, and

represent goals and objectives only.

References in this document to IBM products or services do not imply that IBM intends to make them available in

every country.

The information could include technical inaccuracies or typographical errors. Changes are periodically made to the

information herein; these changes will be incorporated in new editions of

the publication. IBM may make improvements and/or changes in the product(s) and/or the program(s) described in

this publication at any time without notice.

Any references in this information to non-IBM Web sites are provided for convenience only and do not in any

manner serve as an endorsement of those Web sites. The materials at those Web sites are not part of the

materials for this IBM product and use of those Web sites is at your own risk.

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

Overview

Parallel access volumes (PAV) allow your system to access volumes in parallel when you use an I M

System z host.

PAV is a feature of I M 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 I M 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.

ase Volume

I/O

Alias

I/O

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

Prerequisites and Activation of the z/VSE PAV Support

• PAV feature purchased, installed and enabled on the I M System Storage Disk system.

( DS8000 Series Feature Codes 78xx / DS6000 Series Feature Codes 51xx )

• ase and alias devices defined in the System z IOCDS.

( ase and alias devices are transparent to the IOCDS, and therefore both fully qualified

IODEVICE definitions in the IOCDS )

• ase device defined in the z/VSE IPL start up procedure.

( corresponding ADD statement )

• Starting of the z/VSE PAV support via SYSDEF SYSTEM,PAV=START command (see

following section)

For more information, examples and a more detailed description about PAV in the z/VSE context please

see z/VSE Administration SC33-8304-02 .

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

New and Extended Commands:

• SYSDEF SYSTEM

• SIR

• VOLUME

• QUERY SYSTEM

SYS EF SYSTEM (new options)

The SYSDEF SYSTEM command has been extented to start/stop PAV processing on the z/VSE system.

AR 0015 1I40I READY

sysdef system,pav=Start

sysdef system,pav=Start sysdef system,pav=Start

sysdef system,pav=Start

AR 0028 1K01I ALIAS DEVICE 8 FOR BASE ESTABLISHED

AR 0028 1K01I ALIAS DEVICE E FOR BASE ESTABLISHED

AR 0028 1K01I ALIAS DEVICE 9 FOR BASE ESTABLISHED

AR 0028 1K01I ALIAS DEVICE A FOR BASE ESTABLISHED

AR 0028 1K01I ALIAS DEVICE B FOR BASE ESTABLISHED

AR 0015 1I40I READY

sysdef system,pav=Stop

sysdef system,pav=Stop sysdef system,pav=Stop

sysdef system,pav=Stop

AR 0015 1I40I READY

QUERY SYSTEM (new command / output extension)

The QUERY SYSTEM output will also display the current PAV setting on the z/VSE system.

AR 0015 1I40I READY

query system

AR 0015 …

AR 0015 PARALLEL ACCESS VOLUME (PAV): ACTIVE  ( INACTIVE )

AR 0015 1I40I READY

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

SIR (output extension)

The SIR (SYS) output will identify if PAV has been activated on the z/VSE system.

sir sys

AR 0015 CPUID VM = 000xxxxxxxxx000 VSE = FF03xxxyyyy8000

AR 0015 PROCESSOR = 2009-00 LPAR

AR 0015 VM-SYSTEM = (0 02) USERID = VMCF = ON

AR 0015 CPUs = 0000 Cap. = 00%

AR 0015 PROC-MODE = z/Arch(64-BIT) IPL(200) 0 :40:21 04/10/2008

AR 0015 SYSTEM = z/VSE 4.2.0 28/01/2008

AR 0015 VSE/AF 8.2.0 02/28/2008

AR 0015 VSE/POWER 8.2.0 01/11/2008

AR 0015 IPL-PROC = $IPLESA JCL-PROC = $$JCL

AR 0015 SUPVR = $$A$SUPI TURBO-DISPATCHER (66) ACTIVE

AR 0015 HARDWARE COMPRESSION ENABLED

AR 0015 PAV SUPPORT ACTIVE

PAV SUPPORT ACTIVEPAV SUPPORT ACTIVE

PAV SUPPORT ACTIVE

AR 0015 SEC. MGR. = BASIC SECURITY = ONLINE

…

The SIR SMF

,VSE,cuu output will display the maximum I/O queue for a particular cuu .

The value is only given

• if SMF is activated

(see Hints & Tips for z/VSE on http://www-03.ibm.com/servers/eserver/zseries/zvse/ )

• if a single device is specified

• if the VSE option has been specified

• if cuu is not a PAV base device while PAV is active on the system.

sir smf,vse,261

AR 0015 TIMINGS FOR 261 BASED ON 589 I/O INSTRUCTION

AR 0015 MAXIMUM I/O QUEUE

AR 0015

AR 0015 QUEUED PENDING CONNECT DISCONN DEV.BUSY TOTAL

AR 0015 msec/SSCH msec/SSCH msec/SSCH msec/SSCH msec/SSCH msec/SSCH

AR 0015 0.000 0.000 0.369 0.000 0.000 0.369

AR 0015 1I40I READY

For PAV base devices the SIR SMF,VSE,cuu output will display I/O counts for the associated aliases.

The values are given only

• if PAV is active on the system

• if SMF is activated

• if a single device is specified

• if the VSE option has been specified

An I/O count of “ * “ indicates an overflow [ > 32767 I/O INSTRUCTIONS ].

sir smf,vse,

AR 0015 TIMINGS FOR BASED ON 111 I/O INSTRUCTION

AR 0015 BASE I/O INSTRUCTION

AR 0015 ALIAS 8 0 I/O INSTRUCTION

AR 0015 ALIAS 9 0 I/O INSTRUCTION

AR 0015 ALIAS A 10 I/O INSTRUCTION

AR 0015 ALIAS B 94 I/O INSTRUCTION

AR 0015

AR 0015 QUEUED PENDING CONNECT DISCONN DEV.BUSY TOTAL

AR 0015 msec/SSCH msec/SSCH msec/SSCH msec/SSCH msec/SSCH msec/SSCH

AR 0015 0.004 0.000 5.922 0.000 0.000 5.92

AR 0015 1I40I READY

SMF: Channel Subsystem Monitoring Facility

Facility in the channel subsystem that a program can retrieve measured values on performance (I/O count/ Connect Time…. ) for a designated subchannel.

see Section ‘z/VSE Performance Considerations with PAV’ about possible usage

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

VOLUME (output extension / new option)

The VOLUME has been extended to mark a base volume with PAV active by adding an *B in the “code”

field.

AR 0015 1I40I READY

volume

AR 0015 CUU CODE DEV.-TYP VOLID USAGE SHARED STATUS CAPACITY

....

AR 0015 261 6E 210 -900 VIS001 UNUSED 20 CYL

AR 0015 262 6E 210 -900 VIS002 UNUSED 20 CYL

AR 0015 6E*B

*B*B

*B 2105-000 FRA 40 UNUSED 1001 CYL

....

A new DETAIL option has been implemented to display possible alias devices related to the base.

AR 0015 1I40I READY

volume ,detail

AR 0015 CUU CODE DEV.-TYP VOLID USAGE SHARED STATUS CAPACITY

AR 0015 6E*B 2105-000 FRA 40 UNUSED 1001 CYL

AR 0015 BASE TO 8, E, 9, A, B

BASE TO 8, E, 9, A, BBASE TO 8, E, 9, A, B

BASE TO 8, E, 9, A, B

AR 0015 1I40I READY

Alias devices put in parenthesis do indicate an ALIAS device being NOT OPERATIONAL.

…

AR 0015 6E*B 2105-000 FRA 40 UNUSED 1001 CYL

AR 0015 BASE TO 8, E, 9,

BASE TO 8, E, 9,BASE TO 8, E, 9,

BASE TO 8, E, 9,(

((

(

A)A)

A),

((

( B

))

)

…

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

z/VSE Performance Considerations with PAV

Referring to the basic concept of PAV ( see Chapter “Overview” ) it is obvious that most benefit and better

performance can be achieved by defining alias devices for base devices that have a lot of parallel I/O

ongoing .

 speaking for z/VSE : having multiple tasks/partitions issuing I/O against the same volume.

z/VSE does load levelling for parallel I/O’s by selecting a “free” device among the available base and alias

devices.

To help identifying devices that are candidates to improve performance by using PAV, the output of the

SIR SMF,VSE,cuu command can be used.

Example:

sir smf,vse,261

...

AR 0015 MAXIMUM I/O QUEUE 3

MAXIMUM I/O QUEUE 3MAXIMUM I/O QUEUE 3

MAXIMUM I/O QUEUE 3

...

In this case a maximum of 3 I/O requests were queued to the device at one point in time. One waiting for

the other to complete before the next can be processed.

From a high level perspective the configuration and definition of two aliases for this –then been called

‘base’- device could improve overall system performance and throughput.

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

z/VSE General Concepts / Considerations / Restrictions

• Even if the hardware allows the definition of more than seven alias devices, z/VSE will only

support one base and up to seven alias devices. This takes into account that a PAV enabled control

unit can have a maximum of eight physically CHPID’s configured.

• An alias device number must not be used in any z/VSE IPL context. If an ADD statement for a

later – during PAV activation - identified alias device was specified the ADD’ed device will be

boxed and taken out of any z/VSE processing.

• Alias device numbers are also subject to the z/VSE three digit CUU limitation.

• PAV activation requires to have one ‘spare’ I/O device eligible, thus restricting the z/VSE device

limit to 1023. If 1024 devices are added MSG1YS2I is issued.

• During PAV activation all available alias devices for a base will be considered useable. There is

no support to exclude or only use some of the aliases available.

• PAV activation on a native system or under LPAR may take some time, depending on your I/O

configuration ( ALIAS recognition ).

• A dynamic add of alias devices is not supported. Thus devices becoming active are just ignored.

However, if a base device becomes ready while having PAV support active all corresponding

aliases will be activated, too.

• Alias devices becoming not operational are taken out of PAV processing. As indication the alias

cuu is put in brackets on the VOLUME cuu,DETAIL output.

• Even though an alias is considered somewhat virtual from a z/VSE administrator and operator

point of view, it will make use of copy blocks, channel queue entries and other I/O related

resources like a ‘real’ device. Therefore the allocation of such resources must consider alias

devices.

• For former processing, transparency and due the nature that all alias devices correspond physically

to the same base device any system service and message will make use of the base device (cuu)

only.

• Inactivation of the PAV support via the SYSDEF command can lead to delays as the support is set

inactive only after all I/O’s on all alias devices have been completed.

• PAV processing will not improve performance on a ‘single application’ base.

Start I/O – WAIT – Start I/O ….

Obviously having more tasks in parallel issuing I/O’s against a single device will benefit from

PAV.

• Subsystem Monitoring Facility (SMF) is enabled to collect base device information only.

z/VSE Parallel Access Volume White Paper 12/08/2009

©Andreas Vischer

I M Germany Development & Research GmbH

z/VSE PAV support if running under z/VM (restriction)

Even though the z/VM PAV support is mostly transparent to guest operating systems following

restriction apply:

• Control units having Hyper-PAV and basic PAV support enabled and having z/VM Mdisks

allocated on these volumes ( controlled by z/VM ) do not support basic PAV emulation over

Hyper-PAV and vice-versa!

 aliases attached to z/VSE while Hyper-PAV is active on the corresponding control unit are not

recognized during z/VSE PAV activation.

Comman s relevant for z/VM PAV guest support

o QUERY PAV

o QUERY VIRTUAL PAV

o QUERY CU ….

o SET CU …

For further information please see CP Commands and Utilities Reference SC24- 081-0 ; CP

Planning and Administration SC24- 083-0 .

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