Date: Wed, 12 Feb 1997 15:34:42 +1100 From: Bruce Evans <bde@zeta.org.au> To: freebsd-hackers@freebsd.org, Shimon@i-Connect.Net Subject: Re: Raw I/O Question Message-ID: <199702120434.PAA30454@godzilla.zeta.org.au>
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>For example, we did READ and WRITE to random records in a block device. It's usually a mistake to use the block device . It is not raw. It has a braindamaged default block size (BLKDEV_IOSIZE = 2048). Write errors on it can't be reported to the application. Benchmarks on it aren't interesting. >We see a depression in READ and WRITE performance, until block size >reaches 2K. At this point performance picks up and levels off until >block size reaches 8KB. At this point it starts gradual, linear >decline. 2K is magic (see above). I would expect read and write performance to increase with the size below 2K too. I would expect performance to be abysmal for all sizes unless the controller and drive very low command overhead and/or very effective caching. Bruce
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