Dell EMC Solutions Enabler 9.2 SRDF Family CLI User Guide

Before performing any control operations on a dynamic consistency group, you must understand how the SRDF daemon (storrdfd) maintains consistency protection of an SRDF/Star CG during modification.

• The SRDF daemon must be running locally on the Star control host where the symstar modifycg operation is issued.
• The SRDF daemon on the local host continuously monitors the SRDF/Star consistency group that is being changed.
• The SRDF daemons running on other hosts do the following:
  • On hosts not running GNS, SRDF daemons running on Solutions Enabler versions lower than 7.3.1 stop monitoring the SRDF/Star CG during dynamic modification. These daemons see the old CG definition until the symstar buildcg -update command is issued.

    symstar buildcg -update retrieves the new SRDF/Star CG definition file from the local array and replaces the old CG definition with the updated one on that Star control host.

  • On hosts running GNS, SRDF daemons monitor the consistency group while it is being modified.

    After the SRDF/Star CG definition is modified, the GNS daemon sends the new CG definition file to all hosts local to the workload array.

    Issue the symstar buildcg -update command from only one Star control host attached to each affected remote array.

    Depending on the timing of the GNS updates, there may be a brief period during which the SRDF daemon stops monitoring the SRDF/Star CG while waiting for the updated CG definition to propagate to the local GNS daemon.

    NOTE:

    Do not enable the gns_remote_mirror option in the GNS daemon's options file when using GNS with SRDF/Star. This option is not supported in SRDF/Star environments.

    gns_remote_mirror does not remotely mirror CGs that contain concurrent or cascaded devices. If you are using GNS, enabling the gns_remote_mirror option will not mirror the CG if it includes any devices as listed in the "Mirroring exceptions" in the Dell Solutions Enabler Array Controls and Management CLI User Guide. Refer to the guide for a detailed description of GNS.

    To switch to a remote site, issue the symstar buildcg command to build a definition of the CG at each site in the SRDF/Star configuration.