ZFS option vfs.zfs.cache_flush_disable=1

[Zaphod Beeblebrox]

I think the gravamen of the original question is the effect of
vfs.zfs.cache_flush_disable=1.  You have roughly the following situation:

user writes --->> zfs caches --->> controller cache --->> drive cache --->>
disk

The stated problem was that zfs flushes push not only the zfs caches to the
controller, but also the controller caches to disk.  If the zfs cache flush
is disabled, does that mean, in a period of inactivity, that data written
to zfs will possibly sit in the zfs cache and not make it to disk?