Raid Controller Write Cache setting for WAL and Data

Hello,

Is it safe, to have RAID controller (not BBC) write cache _enabled_
for disks where data are stored and write cache _disabled_ for disks
where WAL segments are stored?
I _can_ afford of loosing some data in case of power failure. But I'm
afraid of having database in unrecoverable state after crash.

fsync = on

I have 4 disks, 2 for WAL (RAID1) and 2 for data (RAID1). WAL and data
are on XFS partitions (nobarrier, noatime).

--
Piotr Gasidło