Home > Storage > PowerMax and VMAX > Data Protection > Dell PowerMax and VMAX All Flash: SRDF/Metro Overview and Best Practices > Understanding the Virtual Witness (vWitness)
While the advantage of the previously described VMAX based witness solutions continues to be the high availability of the VMAX product and which is especially beneficial for the customers with existing VMAX systems, a disadvantage of this approach is the requirement for additional VMAX hardware for new customers. The SRDF/Metro Virtual Witness (vWitness) solution, in contrast, provides alternative witness functionality without requiring additional VMAX hardware. Operationally, virtual and physical witnesses are treated the same by HYPERMAX OS and SRDF/Metro. They each offer equivalent functionality and may be employed independently, simultaneously, and securely. If both array-based witness and vWitness are available, SRDF/Metro will prefer the array-based witness. Note that a vWitness will only be used if an array-based witness is not available.
The benefits of a vWitness configuration are the following:
In addition to the vWitness summary information presented below, a separate configuration document is available on support.emc.com entitled VMAX vWitness Configuration Guide and is focused exclusively on vWitness installation, configuration, and management. See this document for additional vWitness information.
The SRDF/Metro vWitness is available for VMAX storage arrays running HYPERMAX OS 5977 Q3 2016 Service Release and Solutions Enabler/Unisphere for VMAX 8.3 or later. The vWitness will be packaged as a VMware virtual appliance (vApp) for installation directly into the customer environment. This package will support Unisphere for VMAX or Solutions Enabler vApp kits with the Solutions Enabler kit being preferred due to its lower hardware requirements for those not requiring the full management capability of Unisphere for VMAX. Once installed, the vWitness will then be configured using the local Embedded Element Manager (EEM) installed on each pair of VMAX3 or VMAX All Flash arrays.
The vWitness vApp will maintain multiple IP connections to redundant management guests on both the primary and secondary SRDF/Metro managed arrays. These IP connections will use TLS/SSL to ensure secure connectivity between the vWitness and SRDF/Metro paired arrays.
Once IP connectivity has been established to the SRDF/Metro paired arrays, the vWitness(s) may then be configured and maintained using an embedded Solutions Enabler SYMCLI or Unisphere for VMAX 8.3 instance on each array. Using this vWitness management interface, the user may perform the following operations:
Add vWitness: Add a new vWitnesses to the configuration. This will not affect the current Witness protection if so configured. SRDF/Metro will learn about the new vWitness and attempt to connect.
Query vWitness: Query the configuration/state of the vWitnesses.
Suspend vWitness: This will make the vWitness temporally inactive. If the vWitness is servicing an active SRDF/Metro session, a force flag would need to be used. The SRDF/Metro session then becomes witness unprotected until a new witness (if available) is renegotiated what might take up to 5 seconds.
Remove vWitness: SRDF/Metro will be notified about the vWitness removal and break the connection to the removed vWitness. This operation is allowed as long as the vWitness being removed is not currently used by an active SRDF/Metro session.
Note: The SRDF personality of devices may also change as a result of a Witness action (VMAX or vWitness based) to better reflect the current availability of the resulting devices to the host. For example, should the witness determine that the current R2 devices remain host accessible and the R1 devices inaccessible, the current R2 devices will change to R1 as a result. Depending on access/availability, the previous R1 device will also change to R2’s as in the case of a bias change.
The requirements for a vWitness deployment are: