Date: Sat, 5 May 2001 17:47:35 -0600 (MDT) From: Doug Russell <drussell@saturn-tech.com> To: Matt Dillon <dillon@earth.backplane.com> Cc: freebsd-stable <freebsd-stable@FreeBSD.ORG> Subject: Re: soft update should be default Message-ID: <Pine.BSF.4.21.0105051736310.95873-100000@beastie.saturn-tech.com> In-Reply-To: <200105051829.f45ITdC49030@earth.backplane.com>
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On Sat, 5 May 2001, Matt Dillon wrote: > Not only will the hard drive not be able to write the write-cached > data to the media, but IDE hard drives will not guarentee write > ordering either. Someone did a test a while back and found that > under heavy disk loads an IDE drive could hold some of the dirty data > in its cache for an indefinite period of time without writing it out. > i.e. it would write out some of the dirty data but also hold some of it > indefinitely, unwritten. Blech. IDE. Need I say more? :) (Yes, I do have some IDE disks, but I prefer SCSI. Don't we all? :) ) I don't have WCE on any IDE disk i can think of, but I don't normally run it on my SCSIs, either, unless I specifically need the write speed. > So turning on WCE is playing with fire. WCE was mangled because > the drive manufacturers were more interested in posting high transfer > rate numbers for benchmarks then in keeping people's data safe. I > remember when it happened... the day the drive manufacturers started > using their lobotomized SCSI cores internally was the day they realized > they could cache writes. Yes, yes, yes! No argument there. People should realize what they are doing by enabling the write cache, softupdates or no softupdates. > Now, there is an IDE flush command. Theoretically it would be possible > to write out non-conflicting sectors with WCE turned on, then flush > the cache, and repeat. Theoretically it would be possible for a > RAID system with its own battery backed cache to operate with WCE > turned on and flush the disks before the data would be lost from > its own cache. This was my only point/question. The blanket statement that "Softupdates Does Not Work With WCE" is very misleading. Enabling the write cache is always dangerous if it isn't done in the correct environment. (For me, that means either scratch data, or battery backed disks, or both.) An individual's requirements will vary, thus YMMV. :) > Realistically, drive manufacturers rarely test the command set the > drives are supposed to support beyond making sure it works with some > idiotic windows driver, so these cool commands are as likely to crash > the drive then to work as advertised. Isn't that the truth! Later...... <Doug> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
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