Dell SRDF Introduction

Array Witness

When using the Array Witness method, SRDF/Metro uses a third "witness" array to determine the winning side. The witness array runs one of these operating environments:

• PowerMaxOS 6079.xxx.xxx or later
• PowerMaxOS 5978.144.144 or later
• HYPERMAX OS 5977.945.890 or later
• HYPERMAX OS 5977.810.784 with e-Pack containing fixes to support SRDF N-x connectivity
• Enginuity 5876 with e-Pack containing fixes to support SRDF N-x connectivity

The SRDF and NDM Interfamily Connectivity Information defines the operating environments that are valid for each SRDF/Metro configuration.

The Array Witness must have SRDF connectivity to both the R1-side array and R2-side array. SRDF remote adapters (RAs) are required on the witness array with applicable network connectivity to both the R1 and R2 arrays.

For redundancy, there can be multiple witness arrays but only one witness array is used by an individual SRDF/Metro group at any single time. The two sides of the SRDF/Metro group agree on the witness array to use when the devices in the group are ready to transition to the ActiveActive state. If the auto configuration process fails and no other applicable witness arrays are available, SRDF/Metro uses the Device Bias method.

The Array Witness method requires two SRDF groups: one between the R1 array and the witness array, and a second between the R2 array and the witness array. A witness group:

• Is an SRDF group that enables an array to act as a Witness for any or all SRDF/Metro sessions that are connected to the array at the other side of the witness group. The group has no other purpose.
  • There can be only one witness group between any pair of arrays.
  • A witness group does not contain any devices.
  • It is not possible to remove a witness group that is protecting a SRDF/Metro configuration unless there is another Witness that the configuration can use.
• Must be online when required to act as a Witness.

  Both witness groups must be online when the device pairs in the SRDF/Metro configuration become Ready on the SRDF link.

SRDF/Metro management software checks that the Witness groups exist and are online when carrying out establish or restore operations. SRDF/Metro determines which witness array an SRDF/Metro group is using, so it is not necessary to specify the Witness. Indeed, there is no means of specifying the Witness.

When the Array Witness method is in operation, the state of the device pairs is ActiveActive.

If the witness array becomes inaccessible from both the R1 and R2 arrays, the state of the device pairs becomes ActiveBias.