Date: Wed, 12 Nov 1997 09:28:04 -0500 (EST) From: "Adrian T. Filipi-Martin" <atf3r@cs.virginia.edu> To: Tom <tom@sdf.com> Cc: Alfred Perlstein <perlsta@cs.sunyit.edu>, hackers@freebsd.org Subject: Re: LFS system? Message-ID: <Pine.SUN.3.90.971112091841.11574C-100000@stretch.cs.Virginia.edu> In-Reply-To: <Pine.BSF.3.95q.971111225629.7749B-100000@misery.sdf.com>
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On Tue, 11 Nov 1997, Tom wrote: > > On Wed, 12 Nov 1997, Alfred Perlstein wrote: > > > has any though been put towards a log based File system? > > Lots. See mount_lfs code (keep in mind that it doesn't work). Do a > "man -k lfs" to get the whole picture. Yep, lots. Ousterhout, one of the designers of LFS, was at Berkely. I belive the BS support was put in by his group originally. The concept was first implemented under the SPRITE OS. It just hasn't been maintained in the 4.4BSD's though. :-( > > would it be a performance gain at all? i think it could be a major > > improvement on heavily modified file systems for instance on a large News > > server were a sync might take a few seconds to complete. > > Performance gain? I always though LFS files systems were slow, due to > the extra overhead. However, that overhead buys you security, and fast > filesystems checks during start up. LFS is fast for filesystems with lots of write activity. LFS is optimized for large reads and writes by always writing tracks and such in a single pass. Futhermore, disk blocks are never updated, they are just rewitten to a new location. The clean-up you allude to does need to be done asynchronously though by a cleaner-process. It is akin to garbage collection which make alot of people wrongly assume it has bad runtime performance or predictability. The log structure does provide nive data security, but it is also a performance booster. For more info look for a paper called "Breaking the I/O Bottleneck" by Ousterhout, et al. Adrian -- adrian@virginia.edu ---->>>>| If I were stranded on a desert island, and System Administrator --->>>| I could only have one OS for my computer, Neurosurgical Visualzation Lab -->>| it would be FreeBSD. Think about it..... http://www.nvl.virginia.edu/ ->| http://www.freebsd.org/
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