VSAN 6.2 hybrid disk group performance degradation (2146267)
After upgrading a Virtual SAN (VSAN) environment with Hybrid disk groups to version 6.2, some virtual machines resident on VSAN datastores may exhibit poor disk IO performance compared to previous versions of VSAN.
For example, Virtual Machine Read and/or Write IOs may have poor response time than on Virtual SAN 6.1 or Virtual SAN 6.0.
A significantly lower than expected read cache hit ratio is observed on Virtual SAN caching tier.
A higher percentage of IOPS may be observed on capacity tier disks (Magnetic disks) on Hybrid diskgroups when compared to VSAN 6.0 or VSAN 6.1 systems.
The VSAN 6.2 performance issue with hybrid disk groups is resolved in VMware ESXi 6.0 Patch Release ESXi600-201608001.
A hybrid disk group comprises of one Solid State Disks (SSD) for the cache tier and one or more Magnetic HDDs (MDs) for the Capacity tier.
In VSAN 6.2, new data services are introduced. One of these data services is Deduplication and Compression. Deduplication and Compression are not supported for Hybrid VSAN configurations.
This issue is caused by VSAN 6.2 performing low level scanning for unique blocks, which is related to deduplication, can still occur on VSAN hybrid disk groups. This causes performance deterioration on Hybrid Disk groups, as it has a significant read caching performance impact on the SSD cache tier of VSAN disk groups.
This issue affects VSAN 6.2 Hybrid deployments only. This issue is NOT applicable to All Flash VSAN Clusters.
This issue is resolved in VMware ESXi 6.0 Patch Release ESXi600-201608001 available at VMware Patch Downloads. For more information, see: