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Performance Considerations

As customers begin to deploy z/VM 7.2 they might wish to give consideration to the following items.

z13 Architecture Level Set (ALS)

z/VM 7.2 requires a z13-family machine or later. Be sure to read all the installation instructions before proceeding. If you have a zEC12-family machine or earlier, you will need to upgrade your hardware before migrating to z/VM 7.2. Generally the correct order for doing these things is first to upgrade your current z/VM image to work with your proposed new hardware, then to upgrade your hardware, then to upgrade your z/VM image to z/VM 7.2.

For more information, see the z/VM 7.2 page.

TDISK Clearing

In z/VM 7.2 the default for TDISK clearing is changed to "enabled." This helps to make the system more secure at the expense of additional time at IPL before the system is ready to give TDISK to users.

With TDISK clearing enabled, at IPL time CP clears the TDISK space serially, cylinder by cylinder, one cylinder per real I/O. Every time the system finishes clearing ten more cylinders, it adds those cleared cylinders to the pool of TDISK from which users can allocate temporary disks.

In our experiments on a 3906-M05 with a DS8800 disk subsystem, CP could clear about 1000 cylinders per second. Clients can use this rate as an estimator for how long it will take at IPL time for n cylinders of TDISK to become available for users.

To secure the old behavior before upgrading to z/VM 7.2, update your z/VM system configuration file to state FEATURES DISABLE CLEAR_TDISK.

For more information, refer to z/VM CP Planning and Administration in the z/VM library.

System Recovery Boost

In z/VM 7.2 the default for System Recovery Boost is changed to "enabled." This will be relevant for only those z/VM customers who run on subcap machines, which of course have physical cores of type CP. Typically these will be our z/VSE-on-z/VM clients.

To secure the old behavior before upgrading to z/VM 7.2, update your z/VM system configuration file to state FEATURES DISABLE RECOVERY_BOOST.

For more information, refer to z/VM CP Planning and Administration in the z/VM library.

UNPARKING MEDIUM

In z/VM 7.2 the default for unparking is changed to "medium." This was done to stop excessive unparking of vertical-low (VL) logical cores. For rationale, read our article.

To secure the old behavior before upgrading to z/VM 7.2, update your z/VM system configuration file to state SRM UNPARKING LARGE.

For more information, refer to z/VM CP Planning and Administration in the z/VM library.

PAGING63 IPL Parameter

In z/VM 7.2 the PAGING63 IPL parameter is no longer honored. This IPL parameter gave clients a way to use the z/VM 6.3 paging code, in case there were something wrong with the post-6.3 enhancements, such as the use of HyperPAV aliases or the use of High Performance FICON.

For more information, refer to z/VM CP Planning and Administration in the z/VM library.

Client Certificate Verification

z/VM 7.2 contains the z/VM 7.1 TCP/IP PTF that lets the z/VM FTP and SMTP servers verify client certificates. This PTF also changed the default verification behavior for the z/VM Telnet server from CLIENTCERTCHECK NONE to CLIENTCERTCHECK PREFERRED. Customers who are migrating to z/VM 7.2 and who had not explicitly coded the Telnet server's verification behavior will see the change. Performance of the z/VM SSL server is affected.

For more information, read our article.

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