SRDF Links

SRDF links are logical connections between Symmetrix SRDF groups and their ports, which are physically connected by cables, routers, extenders, switches and other network devices.

Note: You should configure two or more SRDF links per SRDF group for redundancy and fault tolerance.

The links between a given pair of Symmetrix arrays in an SRDF solution can use one of the following methods to transmit data:

  • Unidirectional
  • Bidirectional
  • Dual-directional

The location of the R1 and R2 devices and the SRDF group configuration at both ends of the SRDF links determines the direction of the SRDF links.

Link states
SRDF links can be either online or offline.The SRDF links are online when the following occurs:

  • The Symmetrix SRDF ports are operational and enabled on both sides of the SRDF configuration.
  • The external link infrastructure components are operational.


SRDF links are offline if one or more of the following occurs:

  • The SRDF hardware (ports, cables, extenders, routers, and switches) is damaged or disconnected.
  • The SRDF directors are offline.
  • The Symmetrix arrays or devices participating in the SRDF relationship are not configured properly.
  • Any combination of the above.


Automatic recovery after all links fail
If all SRDF links fail, the Symmetrix array remembers the SRDF states of the affected SRDF devices and can automatically restore the devices to these states once the SRDF links become operational.

An SRDF device that is in a Ready state just before all links fail is restored to a Ready state when the SRDF links become operational. Likewise, an SRDF device that is in a Not Ready state before the failure is restored to a Not Ready state once the SRDF links become operational. This behavior is also known as pure Ready state behavior.

Automatic recovery can be toggled in the configuration file. If the Prevent Automatic  Recovery After All Links Fail setting is on in the configuration file, all devices in the corresponding SRDF group remain Not Ready after all links fail. This setting allows you to perform sanity checks, for example, to inspect data on the affected devices after the SRDF links are restored and before the devices are made Ready to the host.

Prior to Enginuity version 5669, this configuration setting was applied at the Symmetrix array level. At Enginuity version 5669 and higher, this setting is available at the SRDF group level.
Note: The device-level pure Ready state behavior does not apply to the SRDF/A mode of operation.

Link states after Symmetrix power cycle
If the Force RAs Offline After Power Up configuration setting is on, the SRDF links remain offline following a Symmetrix power cycle. When set, this forces the SRDF ports offline after a power outage event and protects data in a rolling disaster scenario that can follow a power outage. The Force RAs Offline After Power Up setting is a Symmetrix array-level configuration setting, affecting all SRDF groups configured on a given Symmetrix array.

SRDF hardware and software compression support
Hardware  compression
DMX             : Yes, GigE
VMAX 20K/VMAX     : Yes, GigE
VMAX 40K        : Yes, GigE & Fibre channel

Software compression
DMX              : N/A
VMAX 20K/VMAX     : Yes, GigE & Fibre channel
VMAX 40K        : Yes, GigE & Fibre channel

Make a free website Webnode