sync vs async vs zfs

[Quartz]

I'm trying to spec out a new system that looks like it might be very 
sensitive to sync vs async writes. However, after some research and 
investigation I've come to realize that I don't think I understand 
a/sync as well as I thought I did and might be confused about some of 
the fundamentals.

Can someone point me to a good "newbie's guide" that explains sync vs 
async from the ground up? one that makes no assumptions about prior 
knowledge of filesystems and IO. And likewise, another guide 
specifically for how they relate to zfs pool/vdev configuration?

Thanks in advance.