Date: Tue, 14 Dec 1999 01:04:52 +0000 (GMT) From: Terry Lambert <tlambert@primenet.com> To: noslenj@swbell.net (Jay Nelson) Cc: kris@hub.freebsd.org, chat@FreeBSD.ORG Subject: Re: Log file systems? (Was: Re: dual 400 -> dual 600 worth it?) Message-ID: <199912140104.SAA28673@usr08.primenet.com> In-Reply-To: <Pine.BSF.4.05.9912112245060.2635-100000@acp.swbell.net> from "Jay Nelson" at Dec 11, 99 11:13:32 pm
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> >> Also -- and this is just curiosity, why did we go with soft updates > >> instead of finishing lfs? Aside from the fact that soft updates > >> appears cleaner than lfs, is there any outstanding superiority of one > >> over the other? > > > >These are FAQs - instead of wasting peoples cycles in explaining it again > > I'm sure you're right, but I couldn't find the answer in the FAQ I > supped this morning. Is there a different FAQ? They are FAQs, not "in the FAQ". The archives you should be looking at, and the place you should be asking the question are the freebsd-fs list. Soft Updates was implemented because Whistle paid Kirk to do the work, as well as throwing in some of Julians time and my time in the bargain. The reason for doing the work was to get rid of the UPS circuitry and heavy battery in the next generation Whistle InterJet product. LFS wasn't finished because the implementation is incomplete (but only minorly so), and because it was not kept up to date with VM and other system interface changes (IMO: you change the interface, you're responsible for fixing all the code that uses it). The minor missing piece was a "cleaner" daemon to follow behind and reclaim logs that are no longer referenced by inodes. It's pretty trivial to write one of these. Frankly, logging solves different problems than soft updates, and the technology is orthogonal. Soft Updates solves the metadata ordering problem, without requiring synchronous writes. The LFS solves the fast recovery following a crash problem; it does this at the cost of a latency between when disk space is no longer being used, and when it becomes available for reuse, as well as adding in a certain level of fragmentation (the cleaner also needs to be a defragger, for a small definition of defragger). Soft Updates is capable of being generalized to allow dependencies to span file system layers, including externalizing a generalized transactioning interface to user space (Very Useful). Logging is a raw disk management mechanism. > Still, I didn't find > anything that explained the decision to go with soft updates. Perhaps > I missed the relevant threads. Were they prior to '98? Soft Updates came in because someone paid for its developement; there is a bit of difference between the Ganger/Patt implementation, and the one in FreeBSD, but not a huge amount. It leverages greatly on work Kirk had already done for BSDI and OpenBSD. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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