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8946
March 2nd, 2008 10:00
MD3000i and Multipathing in ESX 3.5
Hello.
We're in trouble setting up multipathing with MD3000i.
We've a dual controller MD3000i, with one Virtual DIsc configured. MD3000i is connected to 2 ESX 3.5 Hosts.
We want to assign a different controller/path to a each ESX Host.
MD3000i is MRU (Most Recent Used) in Path Selection policy in ESX by default, so We're unable to specify the path for each ESX Host. If we change to Fixed (besides we can see error messages in MD3000i log: array not optimal, Volume not on preferred path due to AVT/RDAC failover), after rebooting the ESX Host the policy changes back to MRU again.
When it use MRU, sometimes, it can happen that each host uses a different path, but this is not controlable.
Is it possible to assign a different path to each ESX Host?
Thanks!
dining_philosop
60 Posts
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March 7th, 2008 15:00
There is one of two reasons for getting the virtual disk not on preferred path:
1) You donot have redundant paths from the server to the two controllers on the MD storage as shown in the document
2) You have redundant paths (physical paths), but you have not configured the initiator in the ESX server to have iSCSI sessions through the redundant paths (iSCSI paths).
When you create virtual disks on the MD3000i, it by default assigns virtual disks to controllers in round robin fashion. If a virtual disk assigned to a host cannot be accessed by the host through the controller to which it is connected, the failover code in the ESX kernel (ESX 3.5) will execute an operation to move the virtual disk to the controller through which it has full access to the virtual disk. This is when you get the "Virtual Disk Not on Preferred Path" notification. If you want to run with non-redundant paths, the simple way to fix this is to change the preferred path of the virtual disk. You can do this through the MD storage manager.