ZIL is just a fast place to write the data for sync operations. If everything is working then the ZIL is never read from, ZFS uses RAM as that foreground bit.

ZIL is just a fast place to write the data for sync operations. If everything is working then the ZIL is never read from, ZFS uses RAM as that foreground bit. Async writes on a default configuration don't hit the ZIL, only RAM for a few seconds then disk. Sync writes are RAM to ZIL, confirm write, then RAM to pool.