Date: Fri, 11 May 2001 08:08:43 -0700 From: "Kevin Oberman" <oberman@es.net> To: Leon Breedt <ljb@devco.net> Cc: freebsd-mobile@FreeBSD.ORG Subject: Re: slow IDE performance Message-ID: <200105111508.f4BF8hc01120@ptavv.es.net> In-Reply-To: Your message of "Fri, 11 May 2001 11:28:08 %2B0200." <20010511112808.E8710@shell.devco.net>
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> Date: Fri, 11 May 2001 11:28:08 +0200 > From: Leon Breedt <ljb@devco.net> > Sender: owner-freebsd-mobile@FreeBSD.ORG > > I'm not sure if this was already posted, a search didn't turn anything up. > > On my Thinkpad A20m I experienced insane IDE write slowdowns at some point > in updating to 4.3-RC. I could basically do *nothing* while doing large IDE > transfers. This persisted in -RELEASE and -STABLE. > > A quick query of my friendly committer colleague revealed that ATA write > caching was now disabled by default. > > Enabling it in /boot/loader.conf restored my sanity: > > hw.ata.wc="1" Yes, there was quite a long discussion of it about a month or two ago. Look in the archives of stable for the subject "Significant disk (ATA) slowdown with recent stable". The reason that disk cache was disabled is that many IDE disks are junk and don't deal with cache properly in many respects. As a result, use of write cache is placing the integrity of disk data in doubt and can lead to disastrous failure in the event of unexpected power failure. I see a 400% increase in the time required for some disk write operations with write cache disabled, so I bit the bullet and enabled it on my laptop. It does have a good battery backup, after all, but be sure that you understand the risks involved in the use of write cache on cheap disks. It is VERY dangerous to use write cache on a desktop or server where there is no battery backup. R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-mobile" in the body of the message
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