Date: Thu, 5 Dec 1996 14:32:47 +0100 From: se@freebsd.org (Stefan Esser) To: kuku@gilberto.physik.rwth-aachen.de (Christoph Kukulies) Cc: freebsd-hackers@freefall.freebsd.org Subject: Re: ccd considerations Message-ID: <Mutt.19961205143247.se@x14.mi.uni-koeln.de> In-Reply-To: <199612050844.JAA17324@gilberto.physik.rwth-aachen.de>; from Christoph Kukulies on Dec 5, 1996 09:44:42 %2B0100 References: <199612050844.JAA17324@gilberto.physik.rwth-aachen.de>
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On Dec 5, kuku@gilberto.physik.rwth-aachen.de (Christoph Kukulies) wrote: > > I'm planning to equip my mirror machine (ftp.de.freebsd.org) > with two 3.2 GB Quantum Fireball Tempest drives (any objections?) > and now the question: Hmmm, the Fireball TM are real low end SCSI drives ... They are rotating at 4500 RPM only, and while they are able to deliver some 5MB/s continuosly, you don't want to use them as a "random access" device :) > When configuring a ccd disk would there be any benefit if I > use two controllers (ncr/pci) instead of one? In case of low end drives (with typically less than 100KB of drive cache) I'd use seperate controllers. If one of the drives is transmitting a large block of data, the other one will possibly fill up its buffer and stop reading ahead. You will end up reading 64KB and then waiting for one disk revolution to complete (which takes some 13.3 milliseconds in case of a 4500 RPM drive), putting a limit of some 3MB/s (64KB/(7ms+13ms)) per drive on this configuration. (The 7ms are my estimate for the time to transfer 64KB of data at a 10MHz sync. data rate, or 9.5MB/s + 0.5ms command overhead). This calculation is just a rough estimate, but I'd rather avoid the Fireball TM as a "software RAID" drive. I would not trust it to be as a reliable as a "normal" SCSI drive, and I'd rather use a 4GB Quantum Atlas (and buy another one if the first one really gets filled :) instead of the two low end drives. I surely would opt for a solution that does not require two controllers. How about a Tekram DC390F with three Ultra-WIDE IBM DORS-32160. Those are not exactly high end drives, too, but they are 5400RPM and offer 512KB cache. The 40MB/s Ultra-WIDE transfer rate (soon to be supported by the NCR driver, I received patches from Gerard Roudier who ported it to Linux :) allows for all three drives to operate at full throughput. (The Quantum Fireball TM (3254MB) seems to have an 8bit Ultra-SCSI interface, so you may be able to connect two to one Tekram DC390U. This would cost an estimated 179DM for the controller and 695DM per disk drive. The IBM DORS is 499DM (FAST), 529DM (Ultra) or 535DM (Ultra-WIDE), and you'll need a NCR8100S (or ASUS SC200) for 135DM, or a Tekram DC390U (189DM) or DC390F (259DM) respectively. (The DC390F has the advantage to come with both an 8bit and 16bit internal SCSI cable. The latter must be bought seperately for some other SCSI cards, and adds some $50. If you don't mind to use a flat-ribbon cable to connect external devices, then you can use it for them, too ...) Total cost are some 1600DM with two Quantums and an Ultra SCSI card, 1650DM with two 53c810 NCR cards, and 1630DM, 1780DM and 1860DM for three IBM DORS 2GB and FAST, Ultra or Ultra-WIDE NCR SCSI card. (Prices from ads in c't 12/96: CP (pp.430), HW (p.450) and Sunshine (p.438, current price of the DC390F is 259DM, not 279DM as printed)). Best if you get a price quote for the drives from Alternate (pp. 422) too. I have had nothing but good experiences with them, and if they tell you some device was on stock, then expect it to arrive the other day ;) [Note to readers in far away contries ;) All prices incl. VAT. Multiply by 0.57 to convert into US$ without VAT if you can't make sense of the numbers, else ...] (I'd choose the 3*IBM DORS-U + Tekram DC390U variant, since Ultra-WIDE is soon to be replaceed by Ultra2 + LVD, IMHO. Its just an intermediate step, but Ultra2 will be as fast with a bus of half the width, and LVD will allow for up to 12m (40ft) of SCSI cable length, if all devices on the bus support this new electrical interface. They will fall back to standard single-ended, else, for full compatibility with current drives/controllers.) Well, that is what I would do. But as always: YMMV ... Gruss, STefan
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