Primocache 0.9.9 appears to be free of bugs now and working better and faster than 0.9.8.
Windows 8.1 x64. Samsung 840 SSD 120GB backed by Vertex2 100GB and Vertex1 60 GB. Plus a WD 2 TB spinning disk.
Using SSD Cache (Read-only) 4 GB L2 and 0 L1.
First boot: 1.19 GB total read, 1.12 GB written to L2.
Second boot: 1.14 GB total read, 1.11 GB read from L2.
Cache hit rate 97.53%. Getting slightly better with each reboot.
Impressive! Results for caching a Virtualbox VM on a spinning disk gives a lower cache hit rate but then the VM is constantly assigning new blocks. There is nothing that any cache can do about that. Still, I see a very substantial speed improvement on VMs.
The GUI is stable now. Creating/modifying/removing caches (and cache tasks) works flawlessly. I hereby officially declare PrimoCache a top product.
One remark: as far as I can tell, Primo does not 'trim' blocks on a spinning disk (using R/W RAM cache). I believe that your implementation of 'trim' is to simply not write deleted blocks to the SSD at all. Am I right? If so, then enabling Trim for spinners too would increase speed even further. That's because no writes means no time-consuming seeks on the spinner.