In vSAN (not misspelled) 6.2, dedup and compression was introduced. These features; however, only apply to all-flash configurations and must not be set up on Hybrid environments.
Some customers have experienced performance degradation on 6.2 Hybrid environments when compared to 6.0 or 6.1 performance. Read caching performance degradation can be observed for Hybrid Disk Groups on the SSD cache tier, due to a low level scanning for unique blocks (dedup). Although this is normal for All-Flash environments, it is important to check your hosts participating on a Hybrid Cluster, to make sure this is turned OFF.
To check/change this option, you can use the ESXi Shell or PowerCli.
The setting would show “2” if it is turned ON, and “0” if it is turned OFF. It should be set to “0” for EACH Hybrid host.
ESXi Shell – esxcfg-advcfg -g /LSOM/lsomComponentDedupScanType
PowerCli – Get-VMHost<HostName> | Get-AdvancedSetting –Name LSOM.lsomComponentDedupScanType
ESXi Shell – esxcfg-advcfg -s 0 /LSOM/lsomComponentDedupScanType
PowerCli – Get-VMHost <HostName> | Get-AdvancedSetting -Name LSOM.lsomComponentDedupScanType | Set-AdvancedSetting -Value “0”
Using PowerCli is my preference, since you won’t have to enable SSH on the hosts, and you can use wildcards to check/change all the hosts with little effort.