Rules, restrictions, and guidelines for managing LUs

Rules

  • In a Fibre Channel environment, up to 2,048 LU paths can be defined for one host group, and up to 2,048 LU paths can be defined for one port.
  • In an iSCSI environment, up to 2,048 LU paths can be defined for one iSCSI target, and up to 2,048 LU paths can be defined for one port.
  • Up to 255 host groups can be created for one Fibre Channel port.
  • Up to 255 iSCSI targets can be created for one iSCSI port.
  • For an LDEV with the ALU attribute, you can define the LU path to only one host group.
  • For an LDEV with the ALU attribute, you can define the LU path to only one iSCSI target.

Restrictions

  • You cannot define an LU path to the following types of volumes:
    • Journal volumes
    • Pool volumes
    • External volumes with the data direct mapping attribute
    • LDEVs created from an accelerated compression-enabled parity group
    • Deduplication system data volumes
  • When defining LU paths, you must not use RAID Manager and Device Manager - Storage Navigator at the same time. If both programs are used simultaneously, operations might not be performed in the expected order, and the storage configuration might be defined incorrectly.
  • If an LDEV of the ALU attribute is binding to LDEVs with the SLU attribute, the LU path cannot be removed.
  • To define an LU path between a port and an LDEV that has the T10 PI attribute enabled, the port must have T10 PI mode enabled.

Guidelines

  • Queue depth: To ensure smooth processing at the ports and best average performance, the recommended queue depth setting (max tag count) for VSP Gx00 models and VSP Fx00 models is 1,024 per port and 32 per LDEV. Other queue depth settings, higher or lower than these recommended values, can provide improved performance for certain workload conditions.
    Caution Higher queue depth settings (greater than 1,024 per port) can impact host response times or cause failures such as job abend. Caution must be exercised in modifying the recommended queue depth settings.
  • If you attempt to apply many settings in the LUN Manager windows, the SVP might be unable to continue processing. Therefore, you should make no more than approximately 1,000 settings. Note that many settings are likely to be made when defining alternate paths, even though only two commands are required for defining alternate paths.
  • Do not perform the following when host I/O is in progress and hosts are in reserved status (mounted):
    • Remove LU paths
    • Disable LUN security on a port
    • Change the data transfer speed for Fibre Channel ports
    • Change AL-PAs or loop IDs
    • Change settings of fabric switches
    • Change the topology
    • Change the host modes
    • Remove host groups
    • Remove iSCSI targets
    • Setting command devices
  • When a port has a path defined for an LDEV with the GAD reserve attribute and you need to configure the port (delete a host group, set a command device, or change the host mode, topology, AL-PA, or transfer speed), the operation might fail if you configure more than one port at a time. For ports that have a path defined for an LDEV with the GAD reserve attribute, perform these operations on one port at a time.
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