6.1.1.1 Storage Policy Configuration for Performance Testing
It is also important to recognize that vSAN supports per-object based policies, which impact performance and availability. The policies have previously been discussed in this document and are equally applicable to performance testing. These include:
• VMware vSphere Flash Read Cache™ Reservation – VMware does not recommend using this policy during performance testing of server workloads. Any reservation will reserve a portion of the 70 percent allocation of Flash Read Cache to an object, whether it is needed or not. VMware recommends letting the vSAN algorithms handle read cache reservation automatically. This policy is used by default only for VMware Horizon® 6 when using linked clones with replica objects.
• Stripe Width – Use this policy to test the performance of a single virtual machine/VMDK. This allows the VMDK to be split into multiple components, and allows those components to be spread across the cluster of hosts. VMware recommends setting the stripe width equal to the number of nodes in the cluster, up to the maximum of 12. If testing and performing scale-out performance tests with multiple virtual machines or multiple VMDKs, this policy is not recommended.
• Object Space Reservation – This policy is recommended to encourage even distribution of components through a vSAN cluster, by forcing the vSAN algorithms to take into account the full size of the object when making placement decisions. Using this policy is similar to a lazy zero thick disk format, and has no impact on performance outside of the influence on component placement and distribution.
• Number of Failures-to-Tolerate – VMware recommends keeping and testing with a failure to tolerate setting that adheres to the availability needs of the environment. The default is 1. However, testing is recommended using both policies for comparison.