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From: src@scuzzy.uucp (Source Admin)
Newsgroups: comp.unix.i386
Subject: Re: SCSI vs ESDI
Message-ID: <1990Jun12.224047.10790@scuzzy.uucp>
Date: 12 Jun 90 22:40:47 GMT
References: <1990May23.151746.18784@cbnewsm.att.com> <186@xstor.UUCP>
Organization: Scuzzy Research Center (SRC)
Lines: 37

especially on unix (or other multiuser/tasking systems scsi is a win when:
- the scsi adapter is clever (==has its own cpu, ram etc)
  and is a DMA bus master that copies data by iself,
  thereby offloading the main cpu a lot. also the disks
  can work all at the same time.
- you have two or better more disks (and a streamer perhaps)
  preferably with cache/read-ahead/request queues
- concurrent disk intensive processes run (said before)
- the organization is good.

for example my system looks like this:

/         (/dev/dsk/0s1    ):    44082 blocks     8709 i-nodes
/dos      (/dev/dsk/0p1    ):    42964 blocks    65535 i-nodes
/usr      (/dev/dsk/0s3    ):    83244 blocks    31665 i-nodes
/usr2     (/dev/dsk/0s4    ):   179064 blocks    54477 i-nodes
(5MB swap space on disk 0)
/tmp      (/dev/dsk/1s1    ):    49166 blocks    13791 i-nodes
(15MB swap space on disk 1)
/usr/tmp  (/dev/dsk/2s3    ):     3978 blocks      506 i-nodes
/usr/spool (/dev/dsk/2s4    ):    34236 blocks    34681 i-nodes

what's happening on my machine is:
- i have all binaries and nonchanging things on disk 0
- i compile everything on disk 1
- usenet news are on disk 2
- the compiler (gcc) uses /usr/tmp on disk 2
- swapping/paging uses both disk 0 and disk 1 evenly

thus disk intensive actions like compiling don't cause long seeks.
(one disk reads compiler, 'nother r/w's source, third r/w's temp files)
especially unpacking news in the background is a disk hog, so having
a disk for /usr/spool is a real win.
-- 
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