Different ways of configuring PSP RR for your ESX devices.

PSP RR is one of the best PSP(Path Selection Plugin) if you want to leverage multipathing in your SAN environment. PSP_RR  can help you gain higher throughput by scheduling IOs through multiple paths.

I will not discuss performance benefits here as there is a blog already on it. I would like to share information on different ways of configuring PSP RR for your SAN devices.

Currently there are three ways of configuring PSP RR in ESX4.1.
1. Change the default PSP of the SATP claiming your SAN device.  

2. Add a new SATP claimrule with PSP RR for device vendor and model.

3. Add a SATP claimrule with PSP RR with your device name.  

1. Change the default PSP of the SATP claiming your SAN device.

~ #  esxcli nmp satp setdefaultpsp  --satp=VMW_SATP_CX  --psp=VMW_PSP_RR                     

This is the most easiest way of configuring PSP_RR for your devices.By changing the default PSP of the SATP claiming your devices, you can configure all the devices in ESX to use PSP_RR. But this has a side effect. There might be some devices from different array vendor claimed by  the same SATP.This may lead to unexpected performance problems. You should use this option, only when you know what devices will be connected to your ESX host.This method is also documented in VMware KB article.
CleanUp:

Run the same claimrule, with default PSP name for the particular SATP.                                     

esxcli nmp satp setdefaultpsp --satp=VMW_SATP_CX --psp=VMW_PSP_MRU

2. Add a new SATP claimrule with PSP_RR for device vendor and model.
~ # esxcli nmp satp addrule  --satp=VMW_SATP_CX --psp=VMW_PSP_RR --vendor=myVendor  --model=mymodel

This is one of the best option that lets user select a PSP for a specific target.Lets say you have two arrays Array1 and Array2 both claimed by same SATP. If you want the devices corresponding to Array1 to be configured with PSP RR without affecting the devices from Array2, then this is the right option.This is one of the way by which you can mass configure devices with PSP RR for specific target.This will not change the default PSP for the SATP, but will insert a new SATP rule into the SATP rule list, for the target with specific Vendor and Model name.

Cleanup can be done using
 ~ # esxcli nmp satp deleterule  --satp=VMW_SATP_CX --psp=VMW_PSP_RR --vendor=myVendor  --model=mymodel 

3. Add a SATP-PSP claimrule with your device name.

When you have configured MSCS on your ESX host and using some of the LUNs for the MSCS cluster, then above to options are not the right ones. The reason SCSI3 reservations used by MSCS. There is a VMware KB article on this.When you want to configure a few of the specific devices with PSP RR then you can run

~ # esxcli nmp satp addrule  --satp=VMW_SATP_CX --psp=VMW_PSP_RR --device=naa.600a0b8000479284000004f04c8ddfa5
For cleanup:
~ # esxcli nmp satp deleterule  --satp=VMW_SATP_CX --psp=VMW_PSP_RR --device=naa.600a0b8000479284000004f04c8ddfa5

Few things to note.
For all the SATP rules to take effect, unclaim, load and run new SATP rules.
~ # esxcli corestorage claiming unclaim -t location

~ # esxcli corestorage claimrule load

~ # esxcli corestorage claimrule run

Newly added rules will be visible in the satp rule list.

~ # esxcli nmp satp listrules         
                                                                                                                      

The rules will be permanently added to /etc/vmware/esx.conf file.The changes will persist across the reboot.To undo the changes, use the esxcli commands as mentioned above.

Without host profiles you can use GUI to configure PSP RR on device basis only[Option 3].