Date: Mon, 15 May 2000 20:38:05 -0500 From: David Kelly <dkelly@hiwaay.net> To: Ian Cartwright <ICartwright@IT.RJF.com> Cc: "'freebsd-scsi@freebsd.org'" <freebsd-scsi@FreeBSD.ORG> Subject: Re: SCSI Speeds? Message-ID: <200005160138.UAA38353@nospam.hiwaay.net> In-Reply-To: Message from Ian Cartwright <ICartwright@IT.RJF.com> of "Mon, 15 May 2000 10:23:14 EDT." <6D5097D4B56AD31190D50008C7B1579B91204C@EXLAN5>
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Ian Cartwright writes: > My question is this: why does it seem that the slower machine does disk > access much faster? You didn't say how you measured. Others before you have observed IDE drives performing simple tasks faster than SCSI drives. Most notably when running simple operating systems from Microsoft. The consensus is the IDE read/write head is closer to the CPU than with SCSI. That it takes less time to set up an IDE transfer. The downside of IDE is that a drive can only do one thing at a time. And when one drive on the IDE cable is busy the other can not be accessed. Have heard that one day ATA/IDE drives may have SCSI-like multitasking. Its common for IDE drives to cache reads and writes to mask their single tasking nature. Its uncommon to be given any control over this caching, or over bad block management. It *is* common to have this control over SCSI devices. It is also common (but not mandatory) to be able to send multiple commands to a SCSI device before the first command has completed. Just as its common (but not mandatory) for a device to accept a command then step off the bus and allow others to use it while its processing its command(s). Scanners with SCSI interfaces are well known for barely implementing SCSI. If you have a SCSI scanner its best to dedicate a SCSI controller/bus to it. For a single user desktop SCSI is likely not to be the fastest disk solution. But IMHO SCSI devices are more robust because those who choose SCSI are usually more willing to pay for quality, while those who choose ATA/IDE are buying by price. -- David Kelly N4HHE, dkelly@hiwaay.net ===================================================================== The human mind ordinarily operates at only ten percent of its capacity -- the rest is overhead for the operating system. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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