Date: Mon, 26 Aug 2002 18:00:45 -0400 From: Bill Vermillion <bv@wjv.com> To: freebsd-fs@freebsd.org Subject: Re: optimization changed from TIME to SPACE ?! Message-ID: <20020826220045.GB27088@wjv.com> In-Reply-To: <20020826204811.GA337@HAL9000.homeunix.com> References: <31269226357BD211979E00A0C9866DAB02BB998B@rios.sitaranetworks.com> <20020826204811.GA337@HAL9000.homeunix.com>
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-segmentation fault- press any key to reboot Damn damn damn David Schultz said, after restarting his PC and mailer on Mon, Aug 26, 2002 at 13:48 . > Thus spake Chris Ptacek <cptacek@sitaranetworks.com>: > > What actually causes the fragmentation to occur? Read the docs or take a look at one of the books on the BSD file system to explain it fully. > I'm not an expert on FFS, but hopefully someone will correct me if > I have missed something. .... > One problem with fragments is that dealing with them can be > inefficient. If your 9K file grows to a 12K file, then to a 14K > file, then to a 16K file, the filesystem may have to copy > fragments around in order to fit all of the fragments for the end > of the file into a single block. But at the point the files goes to 16K it has no fragmentation at all and there is a good chance those two 8K allocation units will be contiguous. The FFS systme is good at this. > This is the kind of > fragmentation fsck is telling you about. If you have FFS optimize > for space, it will happily manage all of these fragments for you. > If you tell it to optimize for time, FFS will still use fragments, > but it won't bother to keep reallocating them when a file grows; > instead, it will upgrade the file to a full block. The latter > method is more efficient, but you lose a bit more space due to > internal fragmentation. Thus, if FFS expects to run out of space, > or if there are too many free fragments lying around, it will > revert to space optimization until the situation improves. I've been using FFS style systems since about 1993 - and I really like them. If you do get to the poinn where you see optimization changed from time to space - then it's time to get a bigger drive or get rid of some of the cruft. Bill -- Bill Vermillion - bv @ wjv . com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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