vfs.zfs.min_auto_ashift and OpenZFS

[Graham Perrin]

In my sysctl.conf:

vfs.zfs.min_auto_ashift=12

– if I recall correctly, the line was written automatically when I 
installed FreeBSD-CURRENT a year or so ago.

With OpenZFS enabled:

root at momh167-gjp4-8570p:~ # sysctl vfs.zfs.min_auto_ashift
sysctl: unknown oid 'vfs.zfs.min_auto_ashift'

Should I have a different line in sysctl.conf, or is 
vfs.zfs.min_auto_ashift not required with OpenZFS?

Hardware: HP EliteBook 8570p, circa 2013
<https://web.archive.org/web/20150906211950/http://www8.hp.com:80/h20195/v2/GetPDF.aspx/c04163744.pdf>