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Understanding Allocation Classes? (Host, Port)

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The Question is:

Can a port allocation class for a SCSI adapter be set to the same value as the
 system allocation class. Its not clear to me from the docs if allcoation class
 and port allocation class are globally unique or only need to be uniqe within
 each class. E.g.
Can I set ALLOCLASS = 1, PORT allocation class for PKA to 1 and Port allocation
 class for PKB to 51.

The Answer is :

  The OpenVMS Wizard would recommend that the host remain in allocation
  class zero, or that the host be configured in a unique and non-zero
  allocation class.  The OpenVMS Wizard would not generally recommend
  configuring any cluster host and any port in the same allocation class.
  The allocation class mechanism is intended to provide a way to avoid
  device unit number collisions.  Each disk and each tape device in any
  particular (non-zero) disk and tape allocation class -- host or port
  or storage controller -- must have a unique device unit number, across
  all cluster members.
  Any device that is served via multiple hosts (via OpenVMS and a shared
  bus, or via a storage controller) should be configured in the same
  non-zero allocation class.
  Devices in allocation class zero are assumed to be host-local, are
  identified by the host name, and the unit numbers -- which must be
  unique on the local host -- can potentially overlap across hosts.
  Also please see the OpenVMS FAQ section on configuring allocation
  classes and Multi-Path SCSI, and the section on OpenVMS host-based
  volume shadowing (mirroring) and (non-zero) allocation classes.

answer written or last revised on ( 17-JUL-2001 )

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