The ZFS intent log is an example of a supremely disappointing, underwhelming way to integrate SSD storage into your system. Fundamentally, it's just a workaroun

The ZFS intent log is an example of a supremely disappointing, underwhelming way to integrate SSD storage into your system. Fundamentally, it's just a workaround for the fact that most of the write caches preexisting in the storage stack are volatile caches and thus not safe. Putting the ZIL on an SSD allows you to get the safety without sacrificing the performance benefits of the write caching (performance that everyone has come to rely on). But the ZIL doesn't help with read performance, and the data you write to it is never even read unless you have a crash or power failure. And then for the read caching, ZFS has L2ARC as an entirely separate feature. So ZFS does technically have ways to take advantage of SSDs to improve a hard drive storage array—but I don't think anyone would consider it to be an ideal solution, more of a pragmatic minimum viable feature.