I think I finally understand idefix44's question. I'm getting old and slow so please bear with meidefix44 wrote:My request isn't about the cached disk, but to emulate the trim command on the L2 Cache storage disk...
(For the others:) Simply assume that any (true) TRIM command sent by Primo reaches the SSD. If it doesn't, well bad luck but there is little Primo or any other program can do about it.
Then only one question remains: does L2 have the same "Primo-TRIM" (prevent redundant writes) as L1?
Idefix44's findings suggest that it has not. If it were easy, Romex would surely have implemented it. So how does one prevent redundant L2 writes? In case of L1 you can do a quick in-memory compare. For L2 you would need to "remember" block contents by keeping a checksum, to prevent having to read the block from SSD in order to compare it against the block queued for write. But where would you store the checksums to survive a reboot? On L2? Either way L2 optimization is indeed possible but it would take CPU cycles and memory to do the L2 bookkeeping. I think it's very difficult to implement. Yet I'm convinced that Romex will come up with an unexpected and surely clever solution.