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February 09, 2009


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Frank Denneman

After reading your blog, I checked your claim about non-permanent static path selections, but when you create a static path selection with the command excfg-mpath --preferred it will make a permanent configuration. I create a balancing scheme and configured the paths to the managing controller. Specifing different paths for different LUNS. After the boot, the preferred and active path still remain the same configuration.


I never had any of my ESXi hosts change their fixed multipath config after a reboot. Looking at the multipath section in esx.conf I see all luns identified by VML. All hosts have been configured with the VI Client.

G. Mobley

It seems that for those of us with active/passive "midrange" controllers, we can leverage VMware's propensity to use the first enumerated path. By carefully designing the SAN connections and related SAN zoning, we can coax the first enumerated path selection, so we can at least attempt to load balance not only across SAN switches but at least ports 4 ports vs 1. We obviously cannot use a FIXED pathing policy in these active/passive setups or risk LUN thrashing and in my case, the excellent script won't help as we do have access to the Clarion tools.

Consider the following setup:

Hosting Engines
Two HBAs in each hosting machine - one HBA in PCI Slot 4, one HBA in PCI Slot 7

IBM DS4800 / Midrange active/passive controller
Storage Ports - 4, 3, 2, 1 - A Controller
B Controller - Storage Ports - 1, 2, 3, 4

All 8 connections to SAN switches per below...

SAN Switch B Storage Connections
Port 1 - A3, Port 3 - B1
Port 2 - A4, Port 4 - B2

SAN Switch A Storage Connections
Port 1 - A1, Port 3 - B3
Port 2 - A2, Port 4 - B4

Zoning Matrix 1
Switch Zones
A A1, B3
B A3, B1

Zoning Matrix 2
Switch Zones
A A2, B3
B A3, B2

Zoning Matrix 3
Switch Zones
A A2, B4
B A4, B2

Zoning Matrix 4
Switch Zones
A A1, B4
B A4, B1

The following layouts should ~ distribute the initial boot / VMware default pathing across both SAN switches and target controller ports as noted. There are limits based on VMware's requirement that controller A ports always be in a physically lower port #'s than controller B ports on the SAN switches - otherwise, we could split the loading across controller B ports as well (I think..)

The * path should be the first enumerated path...

Host HBA # Switch zMatrix# Zoning
0 4* A* 1 A1*, B3
0 7 B 1 A3, B1

1 7 A 2 A2, B3
1 4* B* 2 A3*, B2

2 4* A* 3 A2*, B4
2 7 B 3 A4, B2

3 7 A 4 A1, B4
3 4 B* 4 A4*,B1

... repeat

I have also included an earlier version below where the 4 controller ports (1,2,3,4) are connected to each Hosting engine, but I'm not sure if that would freak out the storage controllers in the event of a failure being most host ports operate in matched pairs (A1, B1; A2, B2;...) which in the sample case below if we lose a switch, then there is no alternative path for that specific port target but there are other targets..

I'm posting this one simply for discussion but do not plan to implement without further research into storage controller behavior for defined host ports and failover.

Sample showing distribution across all 4 controller ports - not for production
Host HBA # Switch zMatrix Zoning
0 4* A* 1 A1*, B3
0 7 B 1 A4, B2

1 7 A 2 A2, B4
1 4* B* 2 A3*, B1

2 4* A* 3 A3*, B1
2 7 B 3 A2, B4

3 7 A 4 A1, B3
3 4 B* 4 A4*,B2


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