Groups

For detailed information on Symmetrix Groups, refer to the following White Paper: "An Overview of Groups in Symmetrix and Solution Enabler Environments-A detailed Review."

What are the different types of groups used in Symmetrix and Solutions Enabler environments?

There are several types of groups that are commonly used to monitor and control Symmetrix storage. The following are the groups used in Symmetrix:

  • Static SRDF Group: Static SRDF Groups are explicitly configured in the Symmetrix BIN file. These groups can only be created or deleted by using a BIN change. At Enginuity 5x68 and earlier, up to 16 static SRDF Groups can be configured. Beginning with Enginuity 5669, up to 64 Static SRDF Groups can be configured per Symmetrix array.
  • Dynamic SRDF Groups: Dynamic SRDF Groups are created and controlled through EMC host based SRDF software. Dynamic SRDF Groups can be added or deleted dynamically. No BIN file changes are required. Changes made to Dynamic SRDF configurations are persistent through the Symmetrix power cycle and IMPL. They are created and controlled through EMC host-based SRDF software, stored in Symmetrix cache.
  • Device Groups: Symmetrix Device Groups are user-defined objects that are used to view and manage groups of Symmetrix devices. SYMCLI commands can be run against these devices as whole or individual devices with groups. These groups are defined in the SYMAPI configuration database file.
  • Disk Groups: Disk Groups are a group of physical disks that have been created in a Symmetrix BIN file. Disk Groups are formed when  the BIN file is initially written or when additional physical disks are added to the system.
  • Composite Groups: A Composite Group is a user-defined group whose STD device members can belong to multiple Symmetrix arrays and RA groups. These groups are defined in the SYMAPI configuration database file on the host installed with SYMCLI. A Composite Group can be defined as type REGULAR, RDF1, RDF2, or RDF21.
  • RDF Consistency Groups: An RDF Consistency Group is a composite group comprised of RDF devices (RDF1,RDF2, or RDF21 devices) acting in unison to preserve dependent write consistency of a database distributed across multiple SRDF systems. It maintains this consistency by using either EMC PowerPath or Enginuity Consistency Assist (ECA) for SRDF/S or Multisession Consistency (MSC) for SRDF/A.       

SRDF devices with multiple SRDF mirrors
The following rules apply to configuring SRDF groups in multi-site topologies where SRDF devices with two SRDF mirrors are used:

  1. R11 devices must be configured to two SRDF groups at the primary site.
  2. R21 devices and DL R21 devices must be configured to two SRDF groups at the site where the R21 devices and DL R21 devices reside. One SRDF group is paired with an SRDF group at the primary site that contains R1 or R11 devices and another SRDF group is paired with an SRDF group at the tertiary site that contains R2 or R22 devices.
  3. R22 devices at the tertiary site in SRDF/Star topologies must be configured to two different SRDF groups at the tertiary site

Moving dynamic SRDF devices between SRDF groups
With Enginuity versions 5773 or higher, you can move dynamic SRDF devices between SRDF groups without having to process a full synchronization. This feature is helpful when you:

  1. Transition to a different SRDF topology and require minimal exposure on device moveoperations.
  2. Add new SRDF devices to an existing SRDF/A group and require fast synchronization with the existing SRDF/A devices in the group.

 

  • Global Name Services: Group Name Services (GNS) provides a common repository to store and maintain SYMAPI Device Group (DG) and Composite Group (CG) definitions across Symmetrix arrays that are visible to all locally attached hosts. By default, GNS is disabled. The group definitions are stored in the local SYMAPI configuration database file on the host that created the group. Enabling GNS enables group definitions to be stored on the Symmetrix array in a shared GNS repository. This provides redundancy so that if one host goes down, you can still perform SYMCLI control operations from another local host in the Symmetrix environment.
  • Auto Provisioning Groups: Solutions Enabler V7.0 with Enginuity 5874 introduced an easier, faster way to provision storage. Auto Provisioning Groups allow storage administrators to create groups of host initiators, front-end ports, and logical devices. These groups are then associated to form a masking view, from which all controls are managed. Auto Provisioning Groups are not supported on Symmetrix DMX arrays running Enginuity 5773 and earlier.