Date: Thu, 25 Feb 1999 12:25:32 +1100 From: Peter Jeremy <peter.jeremy@auss2.alcatel.com.au> To: ru@ucb.crimea.ua Cc: hardware@FreeBSD.ORG Subject: Re: Tagged queueing and write cache on WDE SCSI drives Message-ID: <99Feb25.121437est.40397@border.alcanet.com.au>
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Ruslan Ermilov <ru@ucb.crimea.ua> wrote: >I have tested all four combinations for Tagged Queueing (TQ) and >Write Cache option (WC). Tagged Queueing is only relevant where a device has a number of outstanding I/O requests. Since your test is single-threaded, it doesn't test TQ. For a realistic TQ test, you need to have a substantial number of processes performing I/O - unfortunately, I don't know of any suitable benchmark. The `seeker' part of bonnie would be the closest. An alternative would be to run a lot of dd's (maybe 20) in parallel. >WC TQ MB/s >======= ======= ==== >OFF OFF 3.9 >OFF ON 4.2 >ON OFF 7.9 >ON ON 4.2 I would expect that enabling WC would improve write speed (which is what dd is testing). I'm surprised by the impact of TQ: Since this is a single-threaded test, it should have negligible impact. It almost looks like something is wrong with the TQ handling in the driver, controller or drive. Peter To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hardware" in the body of the message
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