So say we went for the a minimum 3 devices with expansion to 4 we would need 2 promise cards (each card has 2 channels on which we put only 1 drive each) and 3 IDE drives. Total cost <£300. With a scsi system you would be looking at £700 before you added in a scsi controller.
Almost. Each promise U/33 has two controllers which can support two drives each with the same constraints and speed as modern motherboard PIIX4 chipsets. Interleaved stripe and/or mirror sets yield 2x individual drive r/w performance:
---- U/33 ---- ---- U/33 ---- ide2 ide3 ide4 ide5 M S M S M S M S S1a S2a S1b S2b S3a S4a S3b S4b
I am getting sustained 20MB/s write, 22MB/s read on the 2x7200RPM,14GB IBM drive set on S1a+S1b, 12.5MB/s write, 15MB/s read on the 2x5400RPM,6.4GB IBM drive set on S2a+S2b.
linux RAID0 raidtools-0.50beta10-2. If you add a second Promise U/33 and make all the drives 14GB IBM's, you get 56GB RAID0+1 for about $2500US retail or $0.043/MB
Note that if the stripes are S1a+S2a, S1b+S2b then speed is 1/2 individual drive.
Rgds, Tim.
With regard to performance the lower overhead of IDE actually makes them faster in many cases, especially if as here you only use one device per bus. At the high end you have to go scsi/fibre etc, the biggest boards I've seen have had 20 pci slots, split over a number of seperate busses. That effectively limits you to 40 drives. Driving x pci busses and y cards each with z drives on will also get pretty icky.
Chris
Chris Good - Muscat Ltd. The Westbrook Centre, Milton Rd, Cambridge UK Phone: 01223 715006 Mobile: 07801 788997 http://www.muscat.com