When connecting some storage systems to vSphere, vSphere sometime doesn’t select the most optimal multipathing policy.

I came across the above problem when adding an EMC VPLEX storage system to a  large vSphere 4.1 installation.
vSphere selected the Fixed path multipathing policy. In smaller environments this isn’t normally a problem , but when a Fixed policy is selected in a large environment with multiple datastores. vSphere selects the first path for each datastore, this results in almost all datastores uses the same path. The result is that the path will be overloaded.

EMC’s best practices for EMC VMAX/VPLEX is to use Fixed policy with static load balancing or to use EMC PowerPath.
In our environment Fixed or PowerPath wasn’t an option as we have multiple hosts and datastores, so in close communication with EMC we chose to change the multipathing policy to Round Robin..
EMC has once now informed us that RR is only an option (not the best) if PowerPath or Fixed is not an option.

Changing the policy for a few LUN’s won’t take long, if you only have a few hosts and a few datastores, but if you have multiple hosts with multiple datastores, the task is massive.

Using Powershell and EsxCli the task is very easy and extremely fast.
Thanks to Arnim van Lieshout (http://www.van-lieshout.com/2011/01/esxcli-powercli/) for the basic script.

The below script illustrates how to set RoundRobin and not Fixed, this will be updated ASAP.
Until then take a look at this post from LucD http://communities.vmware.com/message/1774139 

<pre>function FuncMail {
 param($To, $From, $Subject, $Body, $smtpServer)
 $msg = new-object Net.Mail.MailMessage
 $smtp = new-object Net.Mail.SmtpClient($smtpServer)
 $msg.From = $From
 $msg.To.Add($To)
 $msg.Subject = $Subject
 $msg.IsBodyHtml = 1
 $msg.Body = $Body
 $smtp.Send($msg)
}

#load Vmware Module
if ((Get-PSSnapin | Where-Object { $_.Name -eq "VMware.VimAutomation.Core" }) -eq $null) { Add-PSSnapin VMware.VimAutomation.Core }

# ----------- Variables ---------------
#vCenter
$vcServer = "vcenterserver"
$vCenterUser = "vcenterusername"
$vCenterPWD = "vcenterpassword"
$DC = "*" # Use * for all DC else replace * with datacenter name
$cluster = "*" # Use * for all Clusters in DC else replace * with cluster name

# LUN settings
$LUNType = "EMC Fibre Channel Disk*"
$psp = "VMW_PSP_RR"
$satp = "VMW_SATP_INV"
$iops = 10

# ESX
$esxUser = "esxuser-root"
$esxPWD = "esxuserpassword"

# Email
$strEmailTo = "to@mail.com"
$strEmailFrom = "from@mail.com"
$strEmailSubject = "PSP info '$vcServer' "
$strEmailSMTP = "smtpserver.com"

# HTML
$strHeadHTML = "<STYLE TYPE='text/css'>"
$strHeadHTML += "TABLE{border-width: 1px;border-style: solid;border-color: black;border-collapse: collapse;}"
$strHeadHTML += "TH{border-width: 1px;padding: 10px;border-style: solid;border-color: black; background-color:thistle}"
$strHeadHTML += "TD{border-width: 0px;padding: 0px;padding-right: 5px;padding-left: 5px;border-style: solid;border-color: black}"
$strHeadHTML += "</STYLE>"

$strBodyHTMLStart = "<H3> Setting PSP multipath & IOPS : "
$strBodyHTMLStart += Get-Date -Format g
$strBodyHTMLStart += "</H3>"
$strBodyHTMLStart += "<TABLE><TR> <TH>vCenter</TH> <TH>Datacenter</TH> <TH>Cluster</TH> <TH>Host</TH> <TH>Device</TH> <TH>SATP</TH> <TH>Old PSP</TH> <TH>New PSP</TH> <TH>IOPS</TH> <TH>Old Paths</TH> <TH>New Paths</TH></TR>"

$strBodyHTMLinfoStart = "<H3> PSP multipath & IOPS not set : "
$strBodyHTMLinfoStart += Get-Date -Format g
$strBodyHTMLinfoStart += "</H3>"
$strBodyHTMLinfoStart += "<TABLE><TR> <TH>vCenter</TH> <TH>Datacenter</TH> <TH>Cluster</TH> <TH>Host</TH> <TH>Device</TH> <TH>SATP</TH> <TH>PSP</TH> <TH>Paths</TH></TR>"

# ---------- Logic (Don't Change) --------------------

$strBODYHTML = ""
$strBodyExcludeHTML = ""

#Connect to vCenter
Connect-VIServer $vcServer -User $vCenterUser -Password $vCenterPWD| Out-Null

#Get Datacenter Clusters
$arrDC = Get-Datacenter -Name $DC | Sort Name
if($arrDC){
 foreach($objDC in $arrDC){

 #Get Cluster list
 $arrCluster = Get-Cluster -Location $objDC -Name $cluster | Sort name
 if($arrCluster){
 foreach($objCluster in $arrCluster){

 #Connect to ESX hosts in cluster
 foreach ($esx in Get-VMHost -Location $objCluster | Sort Name) {

 Connect-VIServer $esx -User $esxUser -Password $esxPWD | Out-Null

#Retrieve the esxcli instances and loop through them
 foreach($esxcli in Get-EsxCli -Server $esx.name) {

 #Write-Host $esx.Name -BackgroundColor Red

 # Change PSP for EMC VPLEX/VMAX devices
 $arrDevice = $esxCli.nmp.device.list() | where {$_.PathSelectionPolicy -ne $psp -and $_.DeviceDisplayName -like $LUNType}
 if($arrDevice){
 foreach($myDevice in $arrDevice){
 #Write-Host "Updating $($myDevice.Device)" -ForegroundColor green
 $esxCli.nmp.device.setpolicy($null, $myDevice.Device, $psp)
 $esxcli.nmp.roundrobin.setconfig(0,$myDevice.device,[long]$iops,"iops",$false)

 $newPSP = $esxCli.nmp.device.list($myDevice.device)
 $newIOPS = $esxcli.nmp.roundrobin.getconfig($myDevice.device)
 $strBODYHTML += "<TR> <TD>$($vcServer)</TD> <TD>$($objDC.Name)</TD> <TD>$($objCluster.Name)</TD> <TD>$($esx.Name)</TD> <TD>$($myDevice.Device)</TD> <TD>$($myDevice.StorageArrayType)</TD> <TD>$($myDevice.PathSelectionPolicy)</TD> <TD>$($($newPSP[0]).PathSelectionPolicy)</TD> <TD>$($newIOPS.IOOperationLimit)</TD> <TD>$($myDevice.WorkingPaths)</TD> <TD>$($($newPSP[0]).WorkingPaths)</TD></TR>"
 }
 }

 # Changes not set on
 $arrInfoDevice = $esxCli.nmp.device.list() | where {$_.PathSelectionPolicy -ne $psp -and $_.DeviceDisplayName -like $LUNType}
 if($arrInfoDevice){
 foreach($myInfoDevice in $arrInfoDevice){
 $strBODYHTMLinfo += "<TR> <TD>$($vcServer)</TD> <TD>$($objDC.Name)</TD> <TD>$($objCluster.Name)</TD> <TD>$($esx.Name)</TD> <TD>$($myInfoDevice.Device)</TD> <TD>$($myInfoDevice.StorageArrayType)</TD> <TD>$($myInfoDevice.PathSelectionPolicy)</TD> <TD>$($myInfoDevice.WorkingPaths)</TD></TR>"
 }
 }

 #Change the default PSP for my SATP
 $esxcli.nmp.satp.setdefaultpsp($psp,$satp) | Out-Null
 }
 Disconnect-VIServer $esx.name -Confirm:$false
 }
 }
 }
 }
}
#Disconnect from vCenter
Disconnect-VIServer $vcServer -Confirm:$false | Out-Null

$strBodyHTMLEnd = "</TABLE>"
$strBodyHTMLinfoEnd = "</TABLE>"

# Collect the HTML
$strHTML = "<HTML><HEAD>"
$strHTML += $strHeadHTML
$strHTML += "</HEAD><BODY>"
$strHTML += $strBodyHTMLStart
$strHTML += $strBODYHTML
$strHTML += $strBodyHTMLEnd
$strHTML += $strBodyHTMLinfoStart
$strHTML += $strBODYHTMLinfo
$strHTML += $strBodyHTMLinfoEnd
$strHTML += "</BODY></HTML>"

# Email the collected data
FuncMail -To $strEmailTo -From $strEmailFrom -Subject $strEmailSubject -Body $strHTML -smtpServer $strEmailSMTP

Script explained

Line 20-24:
Add you vCenter server name and the logon credentionls.

Line 27-30:
LUNTYPE, is the storage type you want to change PSP and SATP for (you can set this to *, if you want you set the PSP and SATP for all datastores.
PSP, is the multipathing policy you want to change to.
SATP, is the storage array type you want to change the default to.
IOPS, is the number of IO’s to be send, before switching to the next path. vSphere default is 1000, EMC recommends 1, but I found 10 to work for me.
Stephen Foskett has explained what is PSP and SATP in plain English  http://blog.fosketts.net/2011/06/06/vmware-esx-vsphere-satp-psp-support-matrix/.

Line 33-34:
Change the user to a user with root privileges.
Change the password to correspond with the user.

Line 37-40:
Change the info to receive an report of what has been changed.

Line 92-93:
Sets the PSP and IOPS for each datastore.

Line 95-96:
Retrieves the new settings (for verification) for  each datastore.

Line 101-107:
Generates a list of datastores, where the PSP setting wasn’t able to be set.
Run the script again to set them.

Line 111:
Sets the hosts default datastore PSP and SATP.
If your hosts connect to multiple different storage systems, I wouldn’t recommend setting this, but it’s to you.

If you want to see an output on the screen of the progress of the script, uncomment the lines 85, 91

Download the full RoundRobin script here.

An exampel of what a report can look like:

Post is updated after input from Josh Coen, www.valcolabs.com.