Quote Originally Posted by Ao1 View Post
There are still a lot of unknown's. Can SF write combine with no [onboard] cache? If they can do they need a high QD? Can SF only compress xfers above a certain size? How random does the data have to be? What is the ratio between compressibility of data and WA?

@ Anvil, a special version of ASU that could drip feed xfers at specific sizes might help to isolate exactly how the SF controller works.
A wild guess is that it can write combine as it can easily use the SRAM allocated for archiving as a buffer, something like "if size<32K and not timeout, then wait, else archive and flush". The controller does not use external memory but any quantity of internal memory could be used as a buffer. Also... strange things @ Sandforce second generation: my workload is over 50% database related and this translates to about 150GB of writes in a "job" that runs for a few hours. During job run, I see WA of around 0.2-0.3. However, in idle (complete Christmas holiday) I saw WA of over 1.5.