RAID15 on two drives?

	Just read a interesting article on RAID15 on two drives:
	http://www.tomshardware.com/newsletter/vol3/24/raid.html

	Apparently it creates virtual RAID1 drives and then a RAID5
	of those drive, which gives you the same capacity as RAID1,
	but with improved performance (with pretty graphs to show this).

	There are two _fascinating_ paragraphs:

	"In theory, the read operation should be just as quick as
	 they are with a RAID 0. Leaving out the sectors used for
	 the parity data, both hard drives are read from simultaneously."

	Which sounds lik something that should be ~trivially possible
	with a RAID1 system.

	"The same happens when writing, or striping, as in RAID 0.
	 However, the system also writes parity data, so that the
	 contents of a hard drive can be restored based on the parity
	 data it contains. The benefit of this approach is that it
	 should take less time to write the parity data than to
	 completely mirror the data in RAID 1."

	Hum.... With two drives unless the 'parity' copy contains
	_all_ of the original data then it cannot work in the case
	of failure.

	Someone is either smoking some of the best crack here, or I'm
	being unusually dense today....

-- 
			David Brownlee - [email protected]