From owner-freebsd-fs Tue Nov 12 23:35:27 2002 Delivered-To: freebsd-fs@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 64EFC37B401 for ; Tue, 12 Nov 2002 23:35:26 -0800 (PST) Received: from pintail.mail.pas.earthlink.net (pintail.mail.pas.earthlink.net [207.217.120.122]) by mx1.FreeBSD.org (Postfix) with ESMTP id 01ACC43E3B for ; Tue, 12 Nov 2002 23:35:26 -0800 (PST) (envelope-from tlambert2@mindspring.com) Received: from pool0207.cvx21-bradley.dialup.earthlink.net ([209.179.192.207] helo=mindspring.com) by pintail.mail.pas.earthlink.net with esmtp (Exim 3.33 #1) id 18Bs3W-00033D-00; Tue, 12 Nov 2002 23:35:23 -0800 Message-ID: <3DD20037.1D11546A@mindspring.com> Date: Tue, 12 Nov 2002 23:33:11 -0800 From: Terry Lambert X-Mailer: Mozilla 4.79 [en] (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: David Schultz Cc: Tomas Pluskal , freebsd-fs@FreeBSD.ORG Subject: Re: seeking help to rewrite the msdos filesystem References: <20021112134213.P32524-100000@localhost> <3DD14AD9.DF8D3580@mindspring.com> <20021113002807.GA4711@HAL9000.homeunix.com> Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-freebsd-fs@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org 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