Re: R.A.I.D boxes

mew_at_world.std.com (Michael E Willett) writes:

>RAID 3 fails on small reads and small writes and RAID 5 handles large and
>small writes poorly, while RAID 7 ... ^^^^^^

Actually, a RAID 5, the Maximum Strategy Gen 4 (which is resold by IBM as the 9570) does large writes as fast in RAID 5 mode as in RAID 3 mode and does large reads faster in RAID 5 mode than in RAID 3 mode. At a sustained rate of about 90 megabytes/second the Gen 4 is the highest bandwidth disk array of which I am aware and it is fastest in RAID 4 mode.

The Gen 4 is intended to storage serve Cray and other large supercomputers for scientific workloads. In the less stratospheric regions are subsystems like the Mylex DAC960P. The DAC960P-3 can sustain 20 megabytes/second for long sequential read operations using seven disk drives each capable of three megabytes/second media transfer rate or, with EDRAM cache memory and 4.3 megabytes/second drives the controller can sustain 30 megabytes/second. Since Mylex sells primarily through OEMs such as IBM, HP, Storage Dimensions, etc.

It would certainly be interesting to know the maximum SUSTAINED bandwidth achievable some other subsystems. Effective (street) price is also an interesting aspect. Customers seem to be interested in $/MB, $/IO and reliability.

-- 
		Dick Wilmot
		Editor, Independent RAID Report
		(510) 938-7425