donderdag, december 14, 2006

VMware: manual multipathing explained

ESX does not support dynamic multipathing. Therefore, manual multipathing must be configured on each ESX host. This is necessary, because if all datastores use the same path, I/O contention can appear. Example: as we are using an IBM DS 8000, we are able to use 8 targets (Storage Processors) on the device. An ESX host itself has 2 HBA’s (vmhba), so in total we have 16 paths to use.

A path is created by combining 3 components: HBA ID, target ID and LUN ID:

vmhbaX:Y:Z, where:

  • X is the HBA ID (example: vmhba1)
  • Y is the Target ID (example: vmhba1:0)
  • Z is the LUN ID (example: vmhba1:0:0)

It is therefore easy to calculate the optimal path (see screenshot below). For the best performance, make sure all paths are divided equally. In our example below, vmhba1 has 4 paths and vmhba2 has 4 paths. Each target has 1 path. There are 8 SAN LUNs configured. When additional LUNs are created, (example: LUN 8), target 0 will get 2 paths, etc.

  • Start the VI client & select a specific host
  • Go to Configuration => Storage and select a datastore
  • Click on properties => Manage paths
  • Make sure FIXED (active/active array) is selected
  • Use the results above to easily set a specific path (example: vmhba1:4:4)
  • Click on Change and select Preferred to activate this path
  • Repeat for all datastores/ESX host
  • Have fun :)

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