Multipath Support for DataCore Servers
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Overview
This section helps you understand how multipath support in DataCore SANsymphony ensures high availability by creating redundant front-end paths between DataCore Servers and virtual disks. It covers automatic path creation, loopback scenarios, supported protocols (Fibre Channel and iSCSI), and the basic configuration required for loopback multipathing.
Multipath Support for DataCore Server
Multipath support is enabled by default for DataCore Servers in order to create highly available front-end paths when mirrored or dual virtual disks are served to DataCore Servers. Redundant paths will be created if a sufficient number of ports exist. Multipathing is supported for Fibre Channel or iSCSI. ALUA is not enabled on DataCore Servers. (Multipath support for the DataCore Server is not configurable and cannot be disabled in DataCore SANsymphony software.)
Virtual disks may also be served to a server that created it. In the case of a mirrored or dual virtual disk, redundant front-end paths will automatically be created from the virtual disk to each DataCore Server that created it. For example, mirrored virtual disk "VD1" is created with storage sources from servers "SSV1" and "SSV2". The mirrored virtual disk "VD1" is served to "SSV1" using the Serve Virtual Disks wizard, which creates two front-end paths from SSV1 initiator ports to SSV1 targets and two front-end paths from the SSV1 initiator ports to SSV2 targets. In this case, the storage source on SSV1 uses both initiator and target ports on the same server to "loopback" the virtual disk and additional paths are created to SSV2 for high availability. This is useful for failover clustering. Also see Serving Virtual Disks for additional information.
Virtual disks can be served via the loopback port, iSCSI, or Fibre Channel. The loopback port (a virtual FC port) can be selected to serve a virtual disk back to a server that created it and in that case is considered a type of Fibre Channel port. Front-end path types cannot be mixed; all must be either Fibre Channel or iSCSI.
Loopback Configuration for iSCSI and Fibre Channel
Some configuration is necessary in order to create front-end paths that use both an initiator and target on the same server in order to "loopback" the virtual disk over iSCSI or Fibre Channel ports. Configuration must be performed before serving virtual disks.
To "loopback" over iSCSI paths:
On each DataCore Server that will be serving virtual disks back to themselves, use the Microsoft iSCSI Initiator to add and log into one or more target ports on the same server. Log in to more than one target port to create redundant front-end paths.
To "loopback" over Fibre Channel paths:
On each DataCore Server that will be serving virtual disks back to themselves, ensure that a sufficient number of Fibre Channels ports exist with both FE and BE port role assigned to them.
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