- Cache Type = “Cache on device hard disk”
The block reservation of “Cache on device hard disk” is ONLY 4KB, and it’s random I/O.
- Cache Type = “Cache on device RAM with overflow on hard disk”
Since “overflow on hard disk” is vhdx format, the block reservation is 2MB & required for sequential I/O, which will provide better performance than legacy local write cache, but it will consume more filesystem usage.
Hence if there’s heavy IOPS occurred on target device, and RAM cache is running out of range, “overflow on hard disk” cache will be generated, which may grow very fast.