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Requirements for using mirroring

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

ThinkSystem SAN Manager ​

  • The Web Services Proxy service must be running.

  • SAN Manager must be running on your local host through an HTTPS connection.
  • SAN Manager must be showing valid SSL certificates for the storage array. You can accept a self-signed certificate or install your own security certificate using SAN Manager and navigating to Certificate > Certificate Management.

Storage arrays​

  • Synchronous mirroring is not supported on the DE2000H.

  • You must have two storage arrays.
  • Each storage array must have two controllers.
  • The two storage arrays must be discovered in SAN 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 11.50. (They can each run different OS versions.) Mirroring setup is different when using SAN Manager 4.1 and earlier versus 4.2 and later, as well as System Manager 11.60.1 and earlier vs 11.60.2 and later.

    • If your controllers are using System Manager 11.50–11.60.1, select the initiator array and click Launch to open the browser-based System Manager and configure mirroring from there.

    • If your controllers are using System Manager 11.60.2 or later, mirroring configuration is performed entirely from SAN Manager 4.2 or later.

  • 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.
  • In a VMWare environment, DE6000 systems must be mirrored with other DE6000 systems. DE2000 and DE4000 systems can be mirrored with DE2000 or DE4000 systems. DE6000 systems do not support mirroring with DE2000 or DE4000 systems in a VMWare environment.

    • This applies to both asynchronous and synchronous mirroring.

    • No such limitations exist in other host OS environments.

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.