I've just exchanged email with my new technical contact at 3ware, and the problem as it's been explained to me will not affect FreeBSD.

Here's the relevant sections from the mail describing the issue:

----8<----

RAID5 writes can result in corrupted parity.  The data itself is not corrupted -- only the parity.  The current Raid5 firmware performs _TWO_ PCI accesses -- one for data, one for parity calculation.  Thus if physical memory has changed before the second PCI access has completed, parity will be corrupted.  This was a very bad oversight and has been corrected in the 7000, which only performs one PCI access.

Linux ext2 FS performs a "fire and forget" on metadata.  (Last write is always the best write)  These writes are asynchronous and never wait for a completion.

----8<----

Since the FreeBSD block driver abstraction guarantees that data will not be changed out from under the driver, there is no opportunity for this limitation of the RAID implementation to cause problems.

Note also that I've been informed that the 7000 series controllers will not require the double-read behaviour, which should improve their RAID5 performance considerably.

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