Low Cache Hit Ratios when Backend Disk is SATA Hard Drive
Local Storage is rarely used in VMware environment. Also even if local storage is used, it is seldom directly connected to the SATA bus on the motherboard, it almost always goes through a RAID controller.
In the rare case when storage is locally attached SATA drive without a RAID controller, cache hit ratios with VirtuCache improves slowly, because the Queue Depth for the SATA HDD as seen in the VMWare kernel is 1. As a result, only 1 IO request at a time is assigned to the HDD. To increase the Queue Depth, the solution is to use a RAID controller for the locally attached SATA Hard Drive.