User manual IBM ZVSE PARALLEL ACCESS

[. . . ] 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. Base Volume Base Volume Alias Alias I/O I/O I/O I/O I/O I/O 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. [. . . ] ( Base and alias devices are transparent to the IOCDS, and therefore both fully qualified IODEVICE definitions in the IOCDS ) Base 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 . ©Andreas Vischer IBM Germany Development & Research GmbH z/VSE Parallel Access Volume White Paper 12/08/2009 New and Extended Commands: · · · · SYSDEF SYSTEM SIR VOLUME QUERY SYSTEM SYSDEF 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 AR 0028 1K01I ALIAS DEVICE AR 0028 1K01I ALIAS DEVICE AR 0028 1K01I ALIAS DEVICE AR 0028 1K01I ALIAS DEVICE AR 0028 1K01I ALIAS DEVICE AR 0015 1I40I READY AR 0015 1I40I READY sysdef system, pav=Stop AR 0015 1I40I READY 778 77E 779 77A 77B FOR FOR FOR FOR FOR BASE BASE BASE BASE BASE 777 777 777 777 777 ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED ESTABLISHED 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): AR 0015 1I40I READY ACTIVE ( INACTIVE ) ©Andreas Vischer IBM Germany Development & Research GmbH z/VSE Parallel Access Volume White Paper 12/08/2009 SIR (output extension) The SIR (SYS) output will identify if PAV has been activated on the z/VSE system. sir sys AR 0015 AR 0015 AR 0015 AR 0015 AR 0015 AR 0015 AR 0015 AR 0015 AR 0015 AR 0015 AR 0015 AR 0015 AR 0015 . . . CPUID VM PROCESSOR VM-SYSTEM CPUs PROC-MODE SYSTEM IPL-PROC SUPVR = = = = = = 000xxxxxxxxx000 2009-00 VSE = FF03xxxyyyy8000 LPAR (0702) USERID = VMCF = ON Cap. = 00% IPL(200) 07:40:21 04/10/2008 4. 2. 0 28/01/2008 8. 2. 0 02/28/2008 8. 2. 0 01/11/2008 JCL-PROC = $$JCL TURBO-DISPATCHER (66) ACTIVE HARDWARE COMPRESSION ENABLED PAV SUPPORT ACTIVE SECURITY = ONLINE 0000 z/Arch(64-BIT) z/VSE VSE/AF VSE/POWER = $IPLESA = $$A$SUPI SEC. = BASIC The SIR SMF1, 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 3 AR 0015 MAXIMUM I/O QUEUE2 AR 0015 AR 0015 QUEUED PENDING CONNECT DISCONN DEV. BUSY AR 0015 msec/SSCH msec/SSCH msec/SSCH msec/SSCH msec/SSCH AR 0015 0. 000 0. 000 0. 369 0. 000 0. 000 AR 0015 1I40I READY TOTAL msec/SSCH 0. 369 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, 777 AR 0015 TIMINGS FOR 777 BASED ON 111 AR 0015 BASE 777 7 AR 0015 ALIAS 778 0 AR 0015 ALIAS 779 0 AR 0015 ALIAS 77A 10 AR 0015 ALIAS 77B 94 AR 0015 AR 0015 QUEUED PENDING CONNECT AR 0015 msec/SSCH msec/SSCH msec/SSCH AR 0015 0. 004 0. 000 5. 922 AR 0015 1I40I READY I/O I/O I/O I/O I/O I/O INSTRUCTION INSTRUCTION INSTRUCTION INSTRUCTION INSTRUCTION INSTRUCTION DEV. BUSY msec/SSCH 0. 000 TOTAL msec/SSCH 5. 927 DISCONN msec/SSCH 0. 000 1 SMF: Channel Subsystem Monitoring Facility Facility in the channel subsystem that a program can retrieve measured values on performance (I/O count/ Connect Time. . . . 2 see Section `z/VSE Performance Considerations with PAV' about possible usage ©Andreas Vischer IBM Germany Development & Research GmbH z/VSE Parallel Access Volume White Paper 12/08/2009 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 volume AR 0015 . . . . 1I40I CUU 261 262 777 READY VOLID VIS001 VIS002 FRA740 USAGE UNUSED UNUSED UNUSED SHARED STATUS CAPACITY 20 CYL 20 CYL 10017 CYL CODE DEV. -TYP 6E 2107-900 6E 2107-900 6E*B 2105-000 *B A new DETAIL option has been implemented to display possible alias devices related to the base. AR 0015 1I40I READY volume 777, detail AR 0015 CUU CODE DEV. -TYP VOLID USAGE SHARED AR 0015 777 6E*B 2105-000 FRA740 UNUSED AR 0015 BASE TO 778, 77E, 779, 77A, 77B AR 0015 1I40I READY STATUS CAPACITY 10017 CYL Alias devices put in parenthesis do indicate an ALIAS device being NOT OPERATIONAL. . . . AR 0015 777 AR 0015 6E*B 2105-000 FRA740 UNUSED 778, 77E, 779, (77A) 77B) A), BASE TO 778, 77E, 779, (77A), (77B) 10017 CYL . . . ©Andreas Vischer IBM Germany Development & Research GmbH z/VSE Parallel Access Volume White Paper 12/08/2009 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 . . . 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. ©Andreas Vischer IBM Germany Development & Research GmbH z/VSE Parallel Access Volume White Paper 12/08/2009 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. [. . . ] 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. [. . . ]