Requirements for using mirroring

If you plan to configure mirroring, keep the following requirements in mind.

SANtricity Unified Manager

Storage arrays

Note: Mirroring is not available on the EF600 storage array.
  • You must have two storage arrays.
  • Each storage array must have two controllers.
  • The two storage arrays must be discovered in Unified Manager.
  • Each controller in both the primary array and secondary array must have an Ethernet management port configured and must be connected to your network.
  • The storage arrays have a minimum firmware version of 7.84. (They can each run different OS versions.)
  • You must know the password for the local and remote storage arrays.
  • You must have enough free capacity on the remote storage array to create a secondary volume equal to or greater than the primary volume that you want to mirror.
  • Asynchronous mirroring is supported on controllers with Fibre Channel (FC) or iSCSI host ports, while synchronous mirroring is supported only on controllers with FC host ports.

Connectivity requirements

Mirroring through an FC interface (asynchronous or synchronous) requires the following:
  • Each controller of the storage array dedicates its highest numbered FC host port to mirroring operations.
  • If the controller has both base FC ports and host interface card (HIC) FC ports, the highest numbered port is on a HIC. Any host logged on to the dedicated port is logged out, and no host login requests are accepted. I/O requests on this port are accepted only from controllers that are participating in mirroring operations.
  • The dedicated mirroring ports must be attached to an FC fabric environment that supports the directory service and name service interfaces. In particular, FC-AL and point-to-point are not supported as connectivity options between the controllers that are participating in mirror relationships.
Mirroring through an iSCSI interface (asynchronous only) requires the following:
  • Unlike FC, iSCSI does not require a dedicated port. When asynchronous mirroring is used in iSCSI environments, it is not necessary to dedicate any of the storage array’s front-end iSCSI ports for use with asynchronous mirroring; those ports are shared for both asynchronous mirror traffic and host-to-array I/O connections.
  • The controller maintains a list of remote storage systems with which the iSCSI initiator attempts to establish a session. The first port that successfully establishes an iSCSI connection is used for all subsequent communication with that remote storage array. If communication fails, a new session is attempted using all available ports.
  • iSCSI ports are configured at the array level on a port-by-port basis. Intercontroller communication for configuration messaging and data transfer uses the global settings, including settings for:
    • VLAN: Both local and remote systems must have the same VLAN setting to communicate
    • iSCSI listening port
    • Jumbo frames
    • Ethernet priority
Note: The iSCSI intercontroller communication must use a host connect port and not the management Ethernet port.

Mirrored volume candidates

  • RAID level, caching parameters, and segment size can be different on the primary and secondary volumes of a mirrored pair.
  • The secondary volume must be at least as large as the primary volume.
  • A volume can participate in only one mirror relationship.
  • For a synchronous mirrored pair, the primary and secondary volumes must be standard volumes. They cannot be thin volumes or snapshot volumes.
  • For synchronous mirroring, there are limits to the number of volumes that are supported on a given storage array. Make sure that the number of configured volumes on your storage array is less than the supported limit. When synchronous mirroring is active, the two reserved capacity volumes that are created count against the volume limit.

Reserved capacity

Asynchronous mirroring:
  • A reserved capacity volume is required for a primary volume and for a secondary volume in a mirrored pair for logging write information to recover from controller resets and other temporary interruptions.
  • Because both the primary volume and the secondary volume in a mirrored pair require additional reserved capacity, you must ensure that you have free capacity available on both storage arrays in the mirror relationship.
Synchronous mirroring:
  • Reserved capacity is required for a primary volume and for a secondary volume for logging write information to recover from controller resets and other temporary interruptions.
  • The reserved capacity volumes are created automatically when synchronous mirroring is activated. Because both the primary volume and the secondary volume in a mirrored pair require reserved capacity, you must ensure that you have enough free capacity available on both storage arrays that are participating in the synchronous mirror relationship.

Drive Security feature

  • If you are using secure-capable drives, the primary volume and the secondary volume must have compatible security settings. This restriction is not enforced; therefore, you must verify it yourself.
  • If you are using secure-capable drives, the primary volume and the secondary volume should use the same drive type. This restriction is not enforced; therefore, you must verify it yourself.
  • If you are using Data Assurance (DA), the primary volume and the secondary volume must have the same DA settings.