Date: Tue, 27 Nov 2001 08:46:22 -0800 From: "Kevin Oberman" <oberman@es.net> To: "Brian T.Schellenberger" <bts@babbleon.org> Cc: Bob Willcox <bob@immure.com>, "Patrick O'Reilly" <patrick@mip.co.za>, Nils Holland <nils@tisys.org>, FreeBSD Question List <freebsd-questions@FreeBSD.ORG> Subject: Re: Softupdates Message-ID: <200111271646.fARGkMd18195@ptavv.es.net> In-Reply-To: Your message of "Mon, 26 Nov 2001 23:57:36 EST." <01112623573601.00696@i8k.babbleon.org>
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> From: "Brian T.Schellenberger" <bts@babbleon.org> > Date: Mon, 26 Nov 2001 23:57:36 -0500 > Sender: owner-freebsd-questions@FreeBSD.ORG > > On Monday 26 November 2001 18:20, Bob Willcox wrote: > > On Mon, Nov 26, 2001 at 09:19:52AM -0500, Brian T.Schellenberger wrote: > > > > [snip] > > > > > Also, you most definately should turn off write-caching if you turn on > > > softupdates. In fact, you should do this anyway: softupdates are really > > > rather safe, but write caching is quite dangerous, and doubly so with > > > softupdates enabled. > > > > > > To do this, set > > > > > > hw.ata.wc=0 > > > > > > in your /boot/loader.conf (assuming IDE devices). > > If you use softupdates *and* enable write caching then you will screw up your > disk with a simple sequence like > > rm -r foo/* > shutdown -p now > > because the softupdates process will just finish writing its updates before > the power is clobbered. > > At least that happens with my hardward, so softupdates is not compatible with > write-cache-enabled. Ugh! This is terrible. The amount of settling time in a shutdown should be more than enough to allow cache to flush to disk. I do the above on either my laptop (more frequent) and desktop systems and see no similar problem. (Note: / is not running softupdates.) > And from what I can tell (no rigorous testing), softupdates w/o write cache > is just as fast as non-softupdates w/ write cache, but lots safer. I know > that I've crashed 8 times in the last 36 hours and I'm darn glad I don't > enable write caching! (Of course that's not the norm, but sometimes I manage > that sort of thing.) I've done some real testing and this is simply not close to true. The difference is quite dependent on the nature of the disk I/O performed, but I see a difference of > 4x for many operations. I have been running with softupdates and write-cache on my laptop and desktop for many months and I've never had a problem. Of course, I've never had my either system crash 8 times in 36 hours. This discussion has taken place before on both STABLE and MOBILE and the people I tend to trust (Soren and Matt Dillon) both run with softupdates and write cache. I'd suggest looking at the archives for their opinions. Note that write cache is once again the default for ATA drives. (Also please be aware that this whole discussion is probably not relevant to SCSI disks.) 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-questions" in the body of the message
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