I have Debian based Openmediavault 3.0 distribution with iscsi plugin based on ietd. Among others, I use it to serve several disks as ISCSI block mode for VMWare servers. It works, however it is getting out of IOPs slowly.
I wanted to add SSD to cache read/write operations.Best if it will provide caching for several disks on single SSD. Unfortunately, I found that open source caching require somehow preparing disks before use and it not working with unmodified RAW storage I have. I cant prepare disks because these disks are VMFS formatted and planned to put back in the server if no caching method will be found.
I wonder if it is possible at all. I can change ISCSI software if needed.