My SCSI RAID10 rack has a dedicated "channel" (if you are referring to the physical cable connecting the drive to the adapter card) for each drive in the rack. They don't share cables in high-end systems, either, especially with SCSI/640. Long before you run into bottlenecks at the drive cables, you will run into a bottleneck at the interface between your adapter card and the motherboard. The only advantage to multiple channels comes from a very efficient write-back cache right on the RAID card.
Tom is comparing drives that you can buy at a place like CompUSA, isn't he? Budget ATA vs. budget SCSI (The Cheetah). Aside from the hot-swap advantage and a bit more throughput, SCSI just wasn't meant for the CompUSA market. It was intended and best suited for high-end applications. SCSI is also quickly being replaced by fiber channel in the very high-end systems, because fiber channel handles 2Gig throughput. You don't pay a dollar-per-gigabyte to get 2 gigs of throughput. And YES, the drives are much different. These drives are much bigger, much faster, many more platters and heads, and very reliable, and VERY expensive. They go through weeks of intensive testing before they are released for use. If you look at the Seagate models in the low-end consumer market and compare ATA and SCSI in the same lines, you'll find that the hardware behind the PCB is identical. I won't disagree that they overprice the SCSI version of that drive, but there really is a lot more "smarts" in a SCSI drive than ATA. A SCSI device isn't just hard drives, but entire arrays can be interfaced with SCSI, and other device types like scanners, printers, etc. are supported. The main advantage to SCSI is that all SCSI devices must be able to function completely independent of any other device. For example, the SCSI command structure allows you to copy data directly from one drive to another without data going through the adapter. A SCSI device can be disconnected and reconnected at will from its host, and as long as the host wasn't in need of something at that moment, nothing is interrupted. Error handling is just as complex, with the drive itself able to mark bad sectors and relocate data to spare sectors, all without causing any transaction delays. In contrast, ATA is watered down to be simple, cheap and mass reproducable. Very dependent on a host to tell it what to do at any given moment, and if you disconnect it, it's lost from the system until reboot (and possibly damaged). When errors occur on an ATA drive, it has very little smarts to handle it. A failing ATA will drag a system to its knees. Yes, SCSI is an old standard, but many standards are just as old and they are still the best choice today. Look at Ethernet! > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Matt > Sent: Wednesday, March 24, 2004 11:07 PM > To: [EMAIL PROTECTED] > Subject: Re: [Declude.JunkMail] Raid Controller > > That's the company that I was told about before. I think you > might be selling serial ATA short though. > > First, these cards have a separate bus for each drive, so a 4 > port serial ATA RAID card can handle much more than any > single drive can push. No issue there. > > Secondly, I've been reading reviews for over a year now on > Tom's hardware that show IDE drives out performing 15K > Cheetahs. This wasn't always the case but it appears that > there has been a lot of effort in the IDE realm and very > little in the SCSI realm. The SCSI protocol is at least a > decade old as well and I see no reason why you should just > simply keep doubling the bus with that technology when you > can pump more data over a simple firewire or USB cable (along > with power). > > The real question though is how well are these drives made in > comparison to the SCSI ones. SCSI is of course just the > interface and has no effect on the reliability of the drive. > It used to be that they just simply engineered the SCSI > drives better, but I don't know that this is entirely the > case now, or at least if there enough of a difference for it > to really matter. The current SATA drives are generally > suggested to be better than IDE, but I wouldn't expect for > one to be as reliable as a drive that costs 4 times as much > if not more. The incremental boost to reliability may also > be moot depending on the application. I plan on having two > different gateway machines that only do scanning. Redundancy > will be achieved with multiple machines each capable of > handling 100% of the total mail volume. If one fails, big > whoop, replace the bad drive and you're back in business. > > Cost becomes an issue for a non-corporate entity, and I can > afford to dedicate more drives to more distinct tasks with > SATA, and therefore I should be able to achieve better performance. > > The only variable for me that needs consideration is whether > or not the current crop of SATA RAID cards are up to the > task. I haven't seen any deep reviews comparing say a 3ware > card to a LSI card. > > Please feel free to tear any of this stuff down. I'm about > to make some purchases myself and I hate making mistakes when > it comes to such investments. > > Matt [AUTOMATED NOTE: Your mail server [63.147.33.8] is missing a reverse DNS entry. All Internet hosts are required to have a reverse DNS entry. The missing reverse DNS entry will cause your mail to be treated as spam on some servers, such as AOL.] --- [This E-mail was scanned for viruses by Declude Virus (http://www.declude.com)] --- This E-mail came from the Declude.JunkMail mailing list. To unsubscribe, just send an E-mail to [EMAIL PROTECTED], and type "unsubscribe Declude.JunkMail". The archives can be found at http://www.mail-archive.com.
