System Managed Mirroring

In this topic:

About system managed mirroring

Enabling/disabling system managed mirroring

Also see:

Port Connections and Paths

About System Managed Mirroring

A multi-copy virtual disk is created from a storage source (disk pool or pass-through disk) from two or three DataCore Servers in the same server group. Data is synchronously mirrored between the servers to maintain redundancy and high availability of the data.

System managed mirroring addresses the complexity of managing multiple mirror paths for numerous virtual disks. This feature also addresses the 256 LUN limitation by allowing thousands of LUNs to be handled per network adapter. The software transports data in a round robin mode through available mirror ports to maximize throughput and can dynamically reroute mirror traffic in the event of lost ports or lost connections.

Mirror paths are automatically and silently managed by the software. The health of ports and virtual disks are monitored system wide. Loss of port connections and virtual disk mirror failures are reported in the System Health tool. Virtual disk status is also reported in Virtual Disk Lists and in Details pages.

The creation and management of mirror connections are based on the mirror role assigned to server ports:

o           Mirror connections are created between server ports in the server group with the mirror role enabled. As many paths as possible are created without reusing ports. For example, if Port 1 on Server 1 can see Port 1 and Port 2 on Server 2 only one path will be created, either Port 1 (Server 1) to Port 1 (Server 2), or Port 1 (Server 1) to Port 2 (Server 2), not both.

o           As new mirror roles are assigned to ports, new mirror connections are created between servers in the group.

o           Mirror connections are automatically changed, as required, based on the addition or removal of server port mirror roles. A minimum of one mirror connection will be maintained for each server; the removal of the last port mirror role will be prohibited to ensure mirror connectivity.


o           The System Managed Mirroring feature is disabled by default. This feature may be enabled or disabled for the server group.

o           Enabling system managed mirroring will remove all existing mirror paths and route mirror traffic through ports configured with the mirror role using general path selection guidelines. After enabling the feature, the Paths tab in Detail pages display only front-end paths; mirror paths are silently managed and not displayed in the DataCore Management Console.

o           VVOL virtual disks created by the VASA provider use system managed mirroring by default. If the feature is enabled, then later disabled for the server group, all virtual disks (including VVOL virtual disks) are converted to use standard mirror paths. After this point, any new VVOL virtual disks created while system managed mirroring is disabled are created using standard mirror paths.

o           Disabling system managed mirroring will not restore the original mirror paths.

o           The mirror role for a port can be removed while system managed mirroring is enabled and virtual disks are using those ports.

o           Only server ports with the mirror role assigned are considered when creating mirror connections:

·            The usual rules for path selections apply to mirror paths when ports are automatically managed. Fibre Channel (FC) is preferred over iSCSI when both are available. Port types are not mixed in mirror paths. Consequentially, when both iSCSI and FC ports exist with the mirror role and sufficient connectivity exists for FC ports, FC will be used exclusively. The iSCSI ports will not be used unless FC ports connections are unavailable. In this case, adding more FC ports with the mirror role will help distribute mirror traffic between the ports, but adding more iSCSI ports with the mirror role will not.

·            In the event of the loss of all FC connections, the software automatically reroutes all virtual disks over available iSCSI connections. When FC connectivity is restored, the software reroutes the virtual disks over FC connections again.

·            Mirror ports are utilized in a 1 to 1 ratio between servers.  For example, if Server1 has four FC ports with the mirror role and Server2 has five FC ports with the mirror role, then one of the FC ports on Server2 will essentially remain unused.  It will remain in reserve until either a loss of connection occurs between the used ports or the mirror port role is removed on one of the used ports. In either case, the reserved port will be substituted to replace the port that was formerly in use.

·            When using iSCSI for mirroring, ensure ports for mirroring are logged in.

o           Redundant mirror paths are created whenever possible.

o           MPIO for mirror paths is supported. The default selection for MPIO with mirror paths is Round Robin.

o           Preferred mirror paths are not supported.

o           Port group settings affecting mirror paths are ignored.

Enabling System Managed Mirroring for New Virtual Disks

Enabling system managed mirroring from the Server Groups tab will affect new virtual disks only. Existing virtual disks will not be affected by this action; read on in the next section for details on enabling the feature for existing virtual disks.

1            In the DataCore Servers Panel, click on the server group to open the details page.

2           In the Advanced Settings area in the Settings tab, select the System Managed Mirroring Enabled check box.

3           Click Apply.

Enabling System Managed Mirroring for Existing Virtual Disks

There are two ways to enable system managed mirroring for existing virtual disks: on the Settings tab in the Virtual Disk Details panel or with PowerShell.

Enabling System Managed Mirroring from Virtual Disk Details

  1. In DataCore Servers Panel or Hosts Panel, expand Virtual Disks and click the virtual disk to open the details page.

  2. On the Settings tab, select the System Managed Mirroring Enabled check box.

  3. Click Apply.

Using PowerShell to Enable System Managed Mirroring

To enable system managed mirroring for an existing virtual disk, use PowerShell to set the MirrorTrunkMappingEnabled parameter of Set-DcsVirtualDiskProperties to true. Refer to the DataCore Cmdlet Reference Guide for details on the MirrorTrunkMappingEnabled parameter.

The following example enables system managed mirroring for a disk named "vdisk1".

Set-DcsVirtualDiskProperties -VirtualDisk vdisk1 -MirrorTrunkMappingEnabled $true