When virtual disks are created or served to a host, automatic path selections will favor Fibre Channel (FC) ports over iSCSI, if both types are available. In some cases, the paths can be modified to use different ports.
Path selections are
always ruled
by the port role, which is used to regulate which ports can be used for
front-end, mirror, and back-end paths. See
Port
Connections and Paths and Assigning
Port Roles and Groups before modifying virtual disk paths.
Mirror
paths cannot be added, removed, or modified for virtual disks in server
groups with system managed mirroring
enabled.
In this topic:
Changing host path access (Read/Write, Read-Only, No Access)
Changing one or both ports in an existing path will result in changing the path. The initiator port and target port for a path must be either all FC or all iSCSI. When changing a path, new port candidates will consist of all eligible ports of the same port type (FC or iSCSI) that are assigned the appropriate port role.
In order to change
from a FC path to an iSCSI path or vice versa, first change one port to
Auto Select. Setting one port
to Auto Select allows either Fibre
Channel or iSCSI ports to be selected for the other port.
To change an existing virtual disk path or LUN:
1 In the Virtual Disk Details page>Paths tab, select the Show only connected ports check box at the bottom of the page to limit the choices.
2 Click on the port for the path that you want to change and select the new port or Auto Select.
3 If necessary, select a new LUN for the target. (Not available for Auto Select.)
4 After all your changes are made, click Apply.
Use these instructions to manually add a virtual disk path.
To add new paths:
1 In the Virtual Disk Details page>Paths tab, click Add Path under the path selections to open the Add Path dialog box.
2 Select the Path type.
3 Select the Show only connected ports check box at the bottom of the page to limit the choices.
4 In the boxes provided, select the Initiator Machine and Initiator Port for the new path.
5 Select the Target Machine and Target Port for the new path.
6 If necessary, select a new LUN for the target. (Only available for front-end paths when a specific initiator and target port is selected; not available for Auto Select.)
7 Click Add.
8 If adding a front-end path and the virtual disk is already served to a host, perform a disk rescan or equivalent actions on the host so that the new paths will be recognized.
Use these instructions to remove an unnecessary virtual disk path.
To remove paths:
1 In the Virtual Disk Details page>Paths tab, right-click on the path to remove and select Remove path.
2 Click Apply.
A preferred path is manually designated as the favored path to use when multiple paths exist. A preferred path will always be used unless it becomes unavailable. When the preferred path becomes unavailable, I/O operations will failover to the alternate path and failback when the preferred path becomes available again.
Before setting a preferred path, see the topic
Port
Connections and Paths to understand how this feature works.
It is very important to know the differences and interactions between
manually designating
a preferred path for a specific virtual disk and the Preferred
Server host setting, which automatically sets the front-end path policy
based on which DataCore Servers
are selected as preferred servers.
ALUA is required for the proper functioning of preferred server and preferred front-end paths. A single path cannot be set as preferred; when a single path is selected, all redundant front-end paths between initiator and target machines are automatically selected to keep them synchronized.
Preferred
mirror paths are not supported in server groups with system managed mirroring
enabled.
To set preferred front-end (FE) or mirror (MR) paths for a virtual disk:
1 In the Virtual Disk Details page>Paths tab, select the Preferred check box of the path to designate as preferred.
2 Click Apply.
When more than one path exists to back-end physical disks, the preferred path to use can be specified. This option is supported for Fibre Channel and not available for iSCSI. The preferred path is set at the physical disk level.
To select a preferred back-end (BE) path:
1 In Physical Disk Details page>Paths tab, select the Preferred check box for the path that you want to use primarily.
2 Click Apply. The state of the preferred path is Active and the state of the other paths is Standby.
Path access to hosts can be changed from the default Read/Write to Read-only or No Access. The No Access option hides the virtual disk on the path so the host will not see the disk through that path. Mirror path access cannot be changed.
To change the path access:
1 In the Virtual Disk Details page>Paths tab, on the host path, under the Access column, select the required access for that path.
2 Click Apply.