Keith,
> With respect to fs block sizes, one thing making discards suck is that > many high capacity SSDs' physical page sizes are larger than the fs > block size, and a sub-page discard is worse than doing nothing. That ties into the whole zeroing as a side-effect thing. The devices really need to distinguish between discard-as-a-hint where it is free to ignore anything that's not a whole multiple of whatever the internal granularity is, and the WRITE ZEROES use case where the end result needs to be deterministic. -- Martin K. Petersen Oracle Linux Engineering
