The SNAPSHOT UPGRADE FEATURE ( SUF ), also referred to as EXTENDED BUFFER MANAGER  ( XBM ), is included as a component in multiple BMC products.

SUF allows the supported BMC utilities to use snapshot technology when processing snapshots. 

Review the following considerations before installing and using SUF :


Upgrading to Coupling Facility (CF) level 22

The XBM CF structure size when using CF level 22 or greater needs an INITSIZE or SIZE of at least 6 MB. BMC recommends you use an INITSIZE or SIZE of at least 8 MB.

Dispatching priority for XBM

BMC recommends setting the dispatching priority of XBM to just below that of VTAM.

The dispatching priority of XBM should be at least equal to the priority for the Internal Resource Lock Manager (IRLM) or the DBMS (whichever has the higher priority).


Not setting XBM to a sufficiently high dispatching priority can negatively affect overall system performance.

Automatic initialization of the XBM subsystem

XBM runs as a formal MVS subsystem and automatically handles its subsystem initialization.

You do not need to add XBM to the SYS1.PARMLIB subsystem name table.


If you add XBM to your Program Properties Table (PPT), do not define XBM as nonswappable. Defining XBM as nonswappable results in incomplete XBM initialization.

SYSTEMS-wide XBM ENQ demotion (PSS component only)

For the PSS component, XBM uses SYSTEMS-wide ENQs to control shared repository access.

At some sites, demoting SYSTEMS-wide ENQs to SYSTEM-wide ENQs to enhance system performance is common practice. However, BMC does not recommend demoting XBM ENQs (major name BMCXBM).

Backing up your repository when upgrading XBM

Back up your repository before you upgrade to a new version or release of XBM . Repository formats are not backward-compatible among XBM versions.

If you do not back up your repository before you upgrade, you can revert to an earlier version of XBM ; however, you must re-create your repository (including management sets, groups, configurations, and any options that you specified). This compatibility issue is not applicable to maintenance upgrades. For example, if you upgrade from 5.1.00 to 5.1.01, the repository formats do not change.

Migrating your repository when upgrading XBM

You will likely reuse the information stored in your repository when you upgrade to a new version of XBM . The repository information includes configurations, management sets, groups, and option settings.

The Installation System generates the $230VSAM job to migrate your old repository information to your new XBM repository:

  • Migrating repositories when upgraded to a new version of XBM (for example, from 5.1.00 to 5.2.00)

    The $230VSAM job that is generated creates JCL that defines a new VSAM repository data set. To migrate your old repository information, use a copy utility (such as IDCAMS REPRO) to copy the old repository information from your old repository data set into the newly created repository data set.


    If you uninstall XBM , the VSAM data set that holds the XBM repository is not removed. This restriction ensures that you do not lose the configurations, management sets, groups, and options settings that are defined in the XBM repository. If you run the $230VSAM job and this VSAM data set already exists, the job will fail; if this problem occurs, complete one of the following actions:

    • Edit the JCL to refer to another data set (and later transfer the contents of the old repository to that data set).

    • Delete the old repository data set (and permanently lose the configurations, management sets, groups, and options that are defined within it).

  • Migrating repositories when upgraded to a new maintenance level of XBM (for example, from 5.1.00 to 5.1.01)

    The $230VSAM job that is generated creates JCL that alters your existing VSAM repository data set. Before submitting this job, make a backup copy of your repository data set in case you need to fall back to an earlier version.

    If you maintained more than one repository data set (as BMC recommends), you need not make a backup copy. Modify the XBM PROC to point to only one of your existing VSAM repository data sets. When you initialize the new version of XBM for the first time, XBM updates the repository information for only the repository data set specified in the PROC. The other repository data set remains unaltered in case you must revert to the earlier version of XBM .

    When you are satisfied that you no longer need the remaining old repository, add that repository data set name to the PROC and restart XBM.

XBM for IMS and Link Pack Area storage

If you are installing XBM for IMS, ensure that the following modules are not in the Link Pack Area (LPA) of main storage: DFSPLDR0, DFSXDL10, DFSAOS60, DFSAOS80, DFSDLOC0, and DFSDLR00.

If the modules are in LPA storage, move the modules before installing XBM for IMS. Otherwise, XBM might fail with an S0C4 abend.

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