Date: Fri, 22 Sep 2000 00:57:55 -0700
From: Peter Wemm <peter@netplex.com.au>
To: Soren Schmidt <sos@freebsd.dk>
Cc: Stephen.Byan@quantum.com (Stephen Byan), mbendiks@eunet.no ('Marius Bendiksen'), fs@FreeBSD.ORG, sos@FreeBSD.ORG, freeBSD-scsi@FreeBSD.ORG
Subject: Re: disable write caching with softupdates?
Message-ID: <200009220757.e8M7vtG46023@netplex.com.au>
In-Reply-To: <200009211502.RAA92422@freebsd.dk>
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Soren Schmidt wrote: > It seems Stephen Byan wrote: > > Marius Bendiksen [mailto:mbendiks@eunet.no] wrote: > > > > > > Contrast this 10% performance hit versus what you get when > > > you disable > > > > caching entirely. > > > > > > I think you will see that on some drives, this may have a greater > > > performance impact than not caching at all. > > > > Perhaps Søren will be kind enough to run the experiment? I'd be interested > > in analyzing cases in ATA drives where flushing delivers worse performance > > than disabling cache. > > Well, I have been toying a bit with this, so far results are just > timing of a make -j16 buildworld on two IBM DJNA drives (ie no tags) > with varius setups. > > ATA driver "as is": > 3602.63 real 0.00 user 2865.62 sys > > ATA driver with flush cache on "BIO_ORDERED": > 3964.18 real 0.00 user 2870.09 sys > > ATA driver with write cache disabled: > 4423.30 real 0.00 user 2871.87 sys > > So, having the write cache there definitly is a win. It is a win only if you do not value your data. I would gladly turn it off. How do we do this right now? (ie: completely off) > I'll try this on TWO IBM DTLA drives with tags enabled and see what gives.. I'm curious to know if tagged queueing compensates for the loss incurred by disabling write caching. Cheers, -Peter -- Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au "All of this is for nothing if we don't go to the stars" - JMS/B5 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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