function Set-VMHostMultipathPolicy {
    param (
        [string]$LunId,
        [string]$PolicyName
    )
    
    Begin {
        function ShowUsage {
        Write-Host @"

NAME
    Set-VMHostMultipathPolicy

SYNOPSIS
    Changes the multi-path policy of specified LUNs.

SYNTAX
    Get-VMHost | Set-VMHostMultipathPolicy [-LunId] <String> [-PolicyName] <String>

DETAILED DESCRIPTION
    Input is provided to this function by passing VMHostImpl objects to it on the
    pipeline. Both the LunId and PolicyName parameters are required. PolicyName
    can be one of three values: fixed, mru, or rr.

"@
        }
        if ( !$LunId ) {
            ShowUsage
            Throw "LunId is a required parameter"
        }
        $ValidPolicies = 'fixed', 'mru', 'rr'
        if ( $ValidPolicies -notcontains $PolicyName ) {
            ShowUsage
            Throw "ValidPolicies must be one of the following: fixed, mru, rr"
        }
    }
    
    Process {
        if ( $_ -isnot [VMware.VimAutomation.Client20.VMHostImpl] ) { continue }
        $HostStorageSystem = Get-View ( $_ | Get-View ).ConfigManager.StorageSystem
        $HostMPPolicy = New-Object Vmware.Vim.HostMultipathInfoLogicalUnitPolicy
        $HostMPPolicy.policy = $PolicyName
        $HostStorageSystem.SetMultiPathLunPolicy( $LunId, $HostMPPolicy )
    }
}