How to disable hard disk write cache?

[Xu Zhe]

Hi, all,

Does anyone knows how to disable write cache of hard disk?

I have found some hints here at Freebsd website:

https://www.freebsd.org/doc/handbook/configtuning-disk.html

However, this seems only work for ATA devices, what about SAS/NLSAS devices
(Meanwhile, it seems that there is no such sysctl in latest Freebsd release,
which is 10.0)?

Any hints are welcomed!

Thanks in advance.
Peter