From: hph@hphbbs.E.open.DE Subject: Re: SCSI Performance (Yet Again) Date: Fri, 27 Aug 1993 07:10:31 GMT
In article <u5oq9B1w165w@xivic.bo.open.de> ws@xivic.bo.open.de (Wolfgang Schelongowski) writes:
>jhenders@jonh.wimsey.bc.ca (John Henders) writes:
>
>...
>> SO far, it seems
>> to me that the theoretical 5.7 meg/sec of the Adaptec is just that,
>> theory, and only a few people get even 1 meg/sec.
>
>The 5.7 MB/sec are the DMA transfer speed. There are other things
>happening on the SCSI-Bus which have to complete before that. If you
>need to know more about what's going on there, RTFM. There's a
>(German) book about the IDE-Interface and SCSI-Bus (Author:
>Friedhelm Schmidt, ISBN: 3-89319-597-1). As it is published by
>Addison-Wesley, you can pester them to have a translation released
>if there is no English book about that subject.
>
>> Again, on my ST, there was a program that bypassed the filesystem
>> completely to test raw disk i/o, and somehow they even made it
>> non-destructive so you didn't have to use a clean partition to do tests.
>> It seems there is no equivalent under *nix.
>
>How about
> date;dd if=/dev/sda of=/dev/null bs=131072 count=512;date
>(This does only a read, you have to save and restore via dd
>if you want to test write. Just be _very_ careful about _where_
>you test ! Maybe you should backup the disk.)
A far better solutions is:
time dd if=/dev/sd? of=/dev/null bs=1b count=10000
time dd if=/dev/sd? of=/dev/null bs=100b count=100
time dd if=/dev/rsd? of=/dev/null bs=1b count=10000
time dd if=/dev/rsd? of=/dev/null bs=100b count=100
You'll then get 4 time-tables which will show, who's the culprit;
either caching or the filesystem-code by using either, both or
none of 'em.
IOzone is quite a rough measurement utility just good enough to do
rough comparisions of different O.S's or disks.
Regards, Peter
-- ####################===============================**************************** # H.P. Heidinger # Call : +49-201-287433 (data) * ~~ HPHBBS ~~ * # Steeler Str. 121 # : V22/32/42bis, 8N1 * UseNet City-Router * # 45138 Essen # E-Mail: hph@hphbbs.E.open.de * for Essen/Germany *