Configuring Tape Drive Preferencing in MIA for Multi-Location VTS Clusters

Products

• MIM Tape Sharing (MIA)
• MIM Resource Sharing (MIM)

Issue/Introduction

In environments with Virtual Tape System (VTS) clusters distributed across multiple physical locations (e.g., Location A and Location B), users may want to ensure that processors running at a specific location prioritize tape drive allocation from the local cluster rather than selecting devices randomly or from a remote location.

By default, MIM's MIA component does not automatically preference local clusters over remote ones based on the processor's location.

Cause

MIA manages the Eligible Device List (EDL) provided by z/OS. Unless explicitly configured, MIA treats all online, managed devices within the EDL as equally eligible for allocation. It does not possess inherent "location awareness" to automatically favor devices based on physical proximity to the processor.

Resolution

To achieve preferencing behavior, you must manually assign preference values to devices on a system-by-system basis. This is accomplished using the `VARY` command with the `PREFERENCE` parameter, typically within the `MIMSYNCH` member using `IFSYS` statements.

Step 1: Identify Local and Remote Device Ranges

Determine the device addresses associated with the VTS cluster at Location A and Location B.

Step 2: Configure System-Specific Preferencing in MIMSYNCH

Use `IFSYS` blocks to ensure that preferencing commands only execute on the systems residing in the corresponding location.

 

Example Configuration:
In this example, System A is local to VTS Cluster A, and System B is local to VTS Cluster B.

/* Preferencing for systems at Location A */
IFSYS SYSTEMA
  @VARY (AddrA),PREFERENCE=10   /* High priority for local Cluster A */
  @VARY (AddrB),PREFERENCE=1    /* Lower priority for remote Cluster B */
ENDIF

/* Preferencing for systems at Location B */
IFSYS SYSTEMB
  @VARY (AddrB),PREFERENCE=10   /* High priority for local Cluster B */
  @VARY (AddrA),PREFERENCE=1    /* Lower priority for remote Cluster A */
ENDIF

Note: In MIA, a higher numeric preference value indicates a higher priority for allocation.

 

Step 3: Verify Configuration

After implementing the changes, you can verify the settings and device status using the following console command:

`F mia_taskname,DISPLAY LOCALUNITS`

Additional Information

Additional Considerations:

• NOTAVAILABLE Status: If certain drives should never be used by a specific system, you can use `VARY (devaddr),NOTAVAILABLE` within an `IFSYS` block to remove them from the allocation list for that system entirely
  
  
• z/OS vs. MIM Commands: Always use the MIM command prefix (e.g., `@VARY`) or the full command `F mia_taskname,VARY xxx` for these operations. Standard z/OS `VARY` commands do not support MIA-specific parameters like `PREFERENCE` or `NOTAVAILABLE`