ISCSI Multipath or MPIO

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On Windows if we want to do multipath IO (Either for iSCSI or for FC disks), then:

1. We need to go to "Add or remove features" (At least for server OS) and enable "Multipath" feature.

   This might require reboot

2. After this feature is installed we need to open "MPIO" utility and enable multipath for iSCSI disks (or FC disks)
3. Then we should open iSCSI initiator and go to Discovery tab to configure one or more discovery portals. While trying to configure portal after entering IP we should click on Advanced. Then change local adapter to "Microsoft iSCSI Initiator" and choose one of the machines source IPs as Initiator IP.
4. We can add more discovery portals of the same storage with different initiator IPs each time
5. Once the portals are added in Discovery tab of iSCSI initiator we should go to Targets tab and see the name of target possible with inactive status. We should click connect button and again enable multi-path for this target in the pop-up dialog box. Further again click advanced and select local adapter as "Microsoft iSCSI initiator". Then choose a pair of IPs as initiator IP / target portal IP.

   Note that if a host has multiple IPs in the same subnet such as 10.20.18.11/24, 10.20.18.12/24, etc. they will all appear as a single target group. Only IPs of different subnet might appear as different target group.

   Active/active multipath requires multiple interfaces with different IPs (different subnets might help even more but one of the subnets without gateway might have to be same as storage subnet). . This is required only if you want to achieve failover in case there is any problem (NIC fail / ethernet cable failure etc.) at source machine side. Secondary IP is not required if we want to fail over to different target IP (eg 10.20.18.12 from 10.20.18.11) within same target group. That is handled automatically.

6. After click connect once, we can click Connect button again for the same target even though the status has changed to Connected from inactive. That we can add more connections to already connected target. This time select a different initiator IP. If available select a different target IP as well.
7. After adding more than one connection we can select target and click on "Properties" button. More than 1 session for the same target should be visible here.

   This properties pop-up also has a second tab "Portal Groups". If we go there we can see all the IPs such as 10.20.18.11, 10.20.18.12, etc. that have been grouped into a single target portal.

   On this properties pop-up there is also a MCS button at bottom. We can use this to change the multipath algorithm such as Round-Robin, Failover only, etc. You can see multiple sessions for this connection in the list below.

8. If we want to see the device names of disks from this multipath target, we can click on "Devices" button on target tab to see the device name and local drive letter, if assigned.
9. For validating whether multipath is working or not we can run below command after above configuration:

   mpclaim -s -d

   This shows the list of all multipath disks by multipath disk ID (Id to be given for other multipath commands), System disk ID (Id that we can see in Disk management), MCS policy for multiple sessions of this target, etc.

10. For more details of a particular disk use:

    mpclaim -s -d <disk-ID>

    where <disk-ID> is the multipath disk ID 1,2, etc. from first column of "mpclaim -s -d" output and not the system disk ID (Second column).

Refer:

• https://www.solutionzone.net/configure-mpio-for-iscsi/

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