Date: Tue, 02 Apr 1996 10:15:54 +0530 From: A JOSEPH KOSHY <koshy@india.hp.com> To: Michael Smith <msmith@atrad.adelaide.edu.au> Cc: hackers@freebsd.org Subject: Re: HDD cpu usage (IDE vs. SCSI). Message-ID: <199604020445.AA210060355@fakir.india.hp.com> In-Reply-To: Your message of "Tue, 02 Apr 1996 11:03:28 %2B0930." <199604020133.LAA08679@genesis.atrad.adelaide.edu.au>
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>>>>>> "ms" == "Michael Smith" >>>>> ms> No, you're not understanding. For a given CPU, IDE will _always_ use more ms> CPU time than SCSI. Period. I'm afraid I don't understand too; I recently had the oppurtunity to examine a Future Domain TMC-1680 card. From what I could see this was an ISA card with no bus-mastering capability. After the card had read in data from the scsi bus, it would interrupt and the CPU had to use PIO to copy data from the card to the system buffers. Why would card yield better CPU utilization than an IDE solution? As I said earlier, there are lots of SCSI cards and disks on the market; the cheaper ones have made quite a number of compromises in order to lower cost. Thats the market reality. IMO, SCSI is not always better than IDE. ms> If you have lots of free CPU, then IDE is fine, but if you feel that your ms> CPU has better things to do with its time than copy data to and from ms> your disk, then SCSI is the only solution that makes sense. The issue really is how much performance you are getting for your rupee. The last time I checked here, a 1-disk SCSI sub-system cost around twice as much as an equivalent IDE 1-disk sub-system. A single user system 1 or 2 disk IDE configuration (used occasionally for a make world) is quite likely to have sufficient idle time to be cost effective. For things like news servers, or NFS servers or machines with large disk space requirements; there is no question, SCSI is the way to go at the moment. Koshy
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