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From: russotto@wam.UMD.EDU
Newsgroups: comp.sys.mac
Subject: Re: Mac II I/O rates vs. block size
Message-ID: <8904270059.AA02169@vs08csc.UMD.EDU>
Date: 27 Apr 89 00:59:36 GMT
References: <39736@think.UUCP>
Organization: University of Maryland, College Park
Lines: 50

In article <39736@think.UUCP> ephraim@think.COM (Ephraim Vishniac) writes:
>
>Several months ago, Ed Darken reported that he'd written a simple
>program to check the Mac's I/O speed and found it execrable,
>independent of I/O block size.  Ed was kind enough to send me his
>code, and I've finally gotten around to investigating his results.
>Alas, I've lost his net address in the meantime, but I thought the
>explanation might be of general interest.
>
>Ed's program pre-allocated a file on disk, then did a series of writes
>to the file.  That is, he did PBCreate, PBOpen, PBAllocate, a series
>of FSWrites, and a PBClose.  Output rates were terrible, down around
>25kB/S on a Mac II with a hard disk.  Varying the block size on the
>FSWrites didn't seem to help at all.
>
>Guessing that FSWrite was doing a series of single-sector writes, I
>modified Ed's program to use PBWrite instead, and I got the following
>results:
>
>        Block size       Output rate (k Bytes / Second)
>        512              26.3
>        1024             51.7
>        1536             60.8
>        2048             93.8
>        4096             142.9
>        8192             177.8
>        16384            206.9
>
>Plainly, FSWrite has serious brain damage.  Fortunately, substituting
>PBWrite is trivial and yields large improvements for larger block
>sizes.
>
>Ephraim Vishniac  /  Internet: ephraim@think.com  / AppleLink: ThinkingCorp
>Thinking Machines Corporation / 245 First Street / Cambridge, MA 02142-1214
>
>	"Arlo Guthrie, it seems, has found what he was looking for:
>		God, and the Macintosh." (Boston Globe)
Since FSWrite is development-system-dependant, could you please
tell us which development system was used?  (I've written several
of those routines to replace the horrible Megamax C routines, and
I don't see how one could mess them up that badly...  Well,
Megamax could... but I use MPW now)


-- 
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	     Matthew T. Russotto
	     russotto@wam.umd.edu