Benchmarking Linux filesystems on software RAID 1 (Lone Wolves)

The kernel's use of deferred writes (held in system ram) is greatly mitigated by the use of a
journaling filesystem. Such filesystems have a large amount of code dedicated to ordering the
writes so that recovery from a power failure is easy.

A volatile write cache on a raid card or individual disk breaks the filesystem's assumptions
about when its write commands are actually complete. 

The situation with individual drives is getting better, as more of them are supporting various
types of cache flush commands, or tagged writes. The cache on a typical hardware raid card is
too large to be flushing on every journal commit, but I don't see why tagged write commands
wouldn't be very useful. However, I am not aware of a card that implements them (or any other
way for the kernel to manage its cache).