Home > Workload Solutions > SQL Server > Best Practices > AMD-Based SQL Server Best Practices on Dell PowerEdge R740 and PowerMax 2000 > Storage Best Practices > Day One Best Practices > VMware ESXi: Round Robin Path Policy
Round Robin path policy defines how to balance I/O load across active storage paths. In this best practice, we changed the Round Robin path policy to optimize performance.
Category | PowerMax Storage |
Product | VMware ESXi |
Type of best practice | Performance Optimization |
Day and value | Day 1, Highly Recommended |
Overview
At the hypervisor layer, ESXi controls the flow of data to and from the server. There are several configuration choices, including Most Recently Used (MRU), Fixed, and Round Robin. In this best practice, we made changes to the Round Robin path policy to optimize data path usage between the PowerEdge servers and the PowerMax storage.
Round Robin automatically rotates through all available paths to distribute the data flow. As PowerMax has all active paths to storage, Round Robin rotates data across those pathways. By default, Round Robin sends 1,000 I/O operations across one path before using the next path. In this best practice, we change the default of 1,000 to 1. With a Round Robin IOPS limit of 1, the paths to storage are rotated more frequently, thus providing a positive impact upon storage performance.
Recommendation
Changing the Round Robin Path Policy to 1 showed a significant improvement in these performance metrics:
NOPM and TPM significantly increased compared to the prior test, indicating that the change to the Round Robin path policy improved performance.
An increase in PowerMax IOPS indicates more efficient use of I/O paths to storage. Optimal path usage benefits the database as the response times for reads and writes decrease.
Server processor utilization can be impacted by default settings that are not optimized. In this case, the default Round Robin setting of 1,000 I/Os before moving to the next path was impacting performance. Changing the Round Robin setting to 1 I/O before moving to the next path resulted in a more frequent path switch rate, thus improving performance. An increase in server CPU utilization indicates less storage wait time and more efficient processor utilization.
PowerMax IOPS significantly increased, indicating that optimizing Round Robin multipathing enabled storage to process more I/Os per second. Both the PowerMax average read and write response times decreased. The combined increase in IOPS and the decreases in response times means that databases can process greater volumes of data at a faster rate.
SQL Server total reads and writes both increased, indicating that the change to the multi-path policy enables greater I/O. Batch Requests per Second also saw a significant increase in T-SQL command batches completing.
Overall, the best practice of changing the Round Robin path policy from 1,000 I/Os to 1 is highly recommended and should be considered as a Day 1 practice as part of initial data provisioning.
Implementation Steps
To configure Round Robin I/O operations from 1,000 to 1, login into the ESXi console and run the following command:
for i in `esxcfg-scsidevs -c |awk '{print $1}' | grep naa.xxxx`; do esxcli storage nmp psp roundrobin deviceconfig set --type=iops --iops=1 --device=$i; done
Verify the change with the following command:
esxcli storage nmp device list
Additional Resources
This best practice was referenced from VMware Multipathing policies in ESXi/ESX and Adjusting Round Robin IOPS limit from 1000 to 1.