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Step 03 -- Setting the MPIO Policy

Overview

The Mulitpath-IO Policy defines how the host distributes IOs across the available paths to the storage. The Round Robin (RR) policy distributes IOs evenly across all Active/Optimized paths. A better Mulitpath-IO Policy, Least Queue Depth (LQD), is similar to RR in that IOs are distributed across all available Active/Optimized paths, however it provides some additional benefits. LQD will bias IOs towards paths that are servicing IO quicker (paths with lesser queues). In the event that one path becomes intermittently disruptive or is experiencing higher latency, LQD will prevent the utilization of that path reducing the effect of the problem path.

The following are the options for the Multipath-IO policy.

Parameter Value Description
FOO Fail Over Only. 
RR Round Robin.
LQD Least Queue Depth.
LB Least Blocks.
None any currently configured default load balance policy.

 

Least Queue Depth (LQD) is the Pure Storage recommended best practice. 


Viewing an individual Pure Storage FlashArray volume's multi-path disk device properties is only possible if a volume is connected using Fibre Channel or iSCSI. If there are not connected volumes to the Windows Server host review the following topics before proceeding:

It is possible to set the MPIO Policies using Windows PowerShell for the Windows Server host before any volumes are connected. If this is the case skip to the Using Windows PowerShell section.

 

Setup using Windows Disk Management

  1. Open Computer Management using the Tools menu in Server Manager. Select Disk Management from the left hand node tree. This will display the currently connected Logical Units (LUNs) to the Windows Server host. 

     
     
  2. Right-Click on Disk 1 (or whatever Disk # represents the newly connected LUN) and select Properties from the menu. This will open the properties dialog for the PURE FlashArray Multi-Path Disk Device. Each of the device paths has a Path State of Active/Optimized

 

Using Windows PowerShell

The below PowerShell shows running the Load Balance Policy cmdlet to retrieving the current Multipath-IO Policy. On a newly installed Windows Server running Get-MSDSMLocalDefaultLoadBalancePolicy results in None because no policy has been set as Multipath-IO has just been installed. 

 

Retrieving the MPIO Policy

The next sections walkthrough each of these management tasks using the graphical user interface (GUI) or Windows PowerShell.

Get-MSDSMGlobalDefaultLoadBalancePolicy

None

 

Setting the MPIO Policy

When setting the load balance policy the -Policy parameter provides a ValidateSet which includes the following:

When using the Windows PowerShell entering tab after the -Policy parameter will cycle through the different options.

The below PowerShell shows setting the new Multipath-IO Policy Load Balance Policy then retrieving it to ensure it was set properly. 

PS C:\> Set-MSDSMGlobalDefaultLoadBalancePolicy -Policy LQD
PS C:\> Get-MSDSMGlobalDefaultLoadBalancePolicy
LQD