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Xref: sserve comp.arch:27939 comp.unix.bsd:7561 comp.os.linux:15022 Newsgroups: comp.arch,comp.unix.bsd,comp.os.linux Path: sserve!manuel.anu.edu.au!munnari.oz.au!uunet!utcsri!torn!nott!cunews!revcan!quantum!danh From: danh@quantum.on.ca (Dan Hildebrand) Subject: Re: IDE faster than Mips SCSI disk Message-ID: <7j+q=2d@quantum.on.ca> Date: Fri, 06 Nov 92 15:08:46 GMT Organization: Quantum Software Systems References: <1992Nov6.033942.21194@ntuix.ntu.ac.sg> Lines: 51 In article <1992Nov6.033942.21194@ntuix.ntu.ac.sg> eoahmad@ntuix.ntu.ac.sg (Othman Ahmad) writes: >These figures are not meant to be a thorough study. More of a provocation >for more soul searching. The widespread belief that SCSI-2 is "defininely >faster than IDE" is questionable, in fact under some circumstances, entirely >false. One significant point you're missing is that IDE drives use the processor to move the data in and out of the controller card, while SCSI on a PC with an Adaptec 1542 or 1742 controller card is a bus master. This fact lets the host processor continue computing while the SCSI card does the data transfer. If the processor is consuming or producing data at near the rate the SCSI card moves it, the resulting pipelining provides in significantly better performance. For a DOS system, which just waits while the disk I/O is in progress, it doesn't make a lot of difference, but with a multitasking OS, or a filesystem which is doing pre-reads and post-writes, the overlap of I/O with computation is a worthwhile goal. >The mips machine under test runs on ultrix. Although it has up to 10Gbyte >of hard-disk, it is not so heavily loaded. We only use it for email and >news feed. Fragmentation can be severe because I cannot even have 32 >megabyte free space in /usr/tmp , only 30 Mbytes. > > IOZONE: Performance Test of Sequential File I/O -- V1.14b (1/31/92) > Operating System: ULTRIX > >IOZONE performance measurements: > 345684 bytes/second for writing the file > 641985 bytes/second for reading the file > >486/33 Maxtor 7120 200Mbyte > >IOZONE performance measurements: > 367586 bytes/second for writing the file > 499942 bytes/second for reading the file Running IOZONE with QNX on an ISA bus, 33 MHz 486 with only the 8K processor cache ( no motherboard processor cache ), I sustain about 1.6 Mbytes / second read and about 800 Kbytes / second write ( 32 Mbyte files ). This is essentially the platter speed of the drive. Of all the IDE drives I've tried so far, the best performance I've seen was about half that on both read and write, respectively. Local bus will help to speed up IDE drives, but local bus will also speed up SCSI. Bus mastering is still the important difference. I suspect a bus mastering IDE controller card could compete with an Adaptec SCSI controller and disk drive. -- Dan Hildebrand email: danh@qnx.com Quantum Software Systems, Ltd. QUICS: danh (613) 591-0934 (data) (613) 591-0931 x204 (voice) mail: 175 Terrence Matthews (613) 591-3579 (fax) Kanata, Ontario, Canada K2M 1W8