I have the same problems.
Server 1 running zfs (also on boot disks), fast read, poor write (& high IO):
A1SRM 2758F
32 GB RAM
SSD 480GB (512 sector size) - ashift 12
Server 2 zunning zfs (not on boot disks), fast read, poor write (& high IO):
A1SRM 2558
32 GB RAM
HD 7,3TB x3 zfs pool (512...