Storage Array Type Plugins (SATP) and Path Selection Plugins (PSP) are part of the VMware APIs for Pluggable Storage Architecture (PSA). The SATP has all the knowledge of the storage array to aggregate I/Os across multiple channels and has the intelligence to send failover commands when a path has failed. The Path Selection Policy can be either “Fixed”, “Most Recently Used” or “Round Robin”.
If a VMware VM is using RDM with All Flash Arrays, then the Round Robin policy should be used. Furthermore, inside the Linux kernel (VM), the noop IO scheduler should be used. Both need to executed for proper throughput.
As a best practice, the preferred method to set Round Robin policy, is to create a rule that will allow any newly added FlashArray device, to automatically set the Round Robin PSP and an IO Operation Limit value of 1. In this blog I’ll refer to the PureStorage array for setting Round Robin policy as well as setting IO limit.
The following command creates a rule that achieves both of these for only Pure Storage FlashArray devices:
esxcli storage nmp satp rule add -s “VMW_SATP_ALUA” -V “PURE” -M “FlashArray” -P”VMW_PSP_RR” -O “iops=1”
This must be repeated for each ESXi host.
This can also be accomplished through PowerCLI. Once connected to a vCenter Server this script will iterate through all of the hosts in that particular vCenter and create a default rule to set Round Robin for all Pure Storage FlashArray devices with an I/O Operation Limit set to 1.
$hosts = get-vmhost
foreach ($esx in $hosts)
$esxcli=get-esxcli -VMHost $esx
$esxcli.storage.nmp.satp.rule.add($null, $null, “PURE FlashArray RR IO Operation Limit
Rule”, $null, $null, $null, “FlashArray”, $null, “VMW_PSP_RR”, “iops=1”, “VMW_SATP_ALUA”,
$null, $null, “PURE”)
It is important to note that existing, previously presented devices will need to be either manually set to Round Robin and an I/O Operation Limit of 1 or unclaimed and reclaimed through either a reboot of the host or through a manual device reclaim process so that it can inherit the configuration set forth by the new rule. For setting a new I/O Operation Limit on an existing device, use the following procedure:
The first step is to change the particular device to use the Round Robin PSP. This must be done on every ESXi host and can be done with through the vSphere Web Client, the Pure Storage Plugin for the vSphere Web Client or via command line utilities.
esxcli storage nmp device set -d naa. –psp=VMW_PSP_RR
Note that changing the PSP using the Web Client Plugin is the preferred option as it will automatically configure Round Robin across all of the hosts. Note that this does not set the IO Operation Limit to 1. That is a command line option only, and must be done separately.
Round Robin can also be set on a per-device, per-host basis using the standard vSphere Web Client actions. The procedure to setup Round Robin policy for a Pure Storage volume. Note that this does not set the IO Operation Limit it 1 which is a command line option only—this must be done separately.
The IO Operations Limit cannot be checked from the vSphere Web Client—it can only be verified or altered via command line utilities. The following command can check a particular device for the PSP and IO Operations Limit:
esxcli storage nmp device list -d naa.
To set a device that is pre-existing to have an IO Operation limit of one, run the following command:
esxcli storage nmp psp roundrobin deviceconfig set -d naa. -I 1 -t iops