Date: Tue, 12 Nov 2002 23:33:11 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: David Schultz <dschultz@uclink.Berkeley.EDU> Cc: Tomas Pluskal <plusik@pohoda.cz>, freebsd-fs@FreeBSD.ORG Subject: Re: seeking help to rewrite the msdos filesystem Message-ID: <3DD20037.1D11546A@mindspring.com> References: <20021112134213.P32524-100000@localhost> <3DD14AD9.DF8D3580@mindspring.com> <20021113002807.GA4711@HAL9000.homeunix.com>
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David Schultz wrote: > > The issue is that UNIX files are accessed by offset, and FAT files > > are accessed by offset by chaining clusters from the start to the > > cluster of interest, and then reading blocks. > = > Few people use FAT filesystems under heavy load as they do UFS. > Basically, I think what he wants to do is speed up sequential > reads for a single process doing, say, digital video editing. On > a FAT FS that is relatively free of fragmentation, na=EFve > read-ahead is likely to improve performance for this type of load, > even though the next logical block in the file might not be the > next physical block on the disk. IIRC, SMARTDRV does this. This > approach is optimizing for the single-user case, but if you have > several people using a single FAT FS at a time, you have much > bigger problems. That's why, in my first posting, I suggested that a one cluster reference cache-behind wasn't really enough to deal with the problem. FWIW, "multiuser" in this context could include multiple applications, such as a playback, a mixer, and an editor, so the "non-multiuser" argument for what you have to worry about on FAT is not a very good argument (or the cache-behind would be enough for sequential access). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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