From owner-freebsd-hackers Wed Nov 3 11:30:18 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from bingnet2.cc.binghamton.edu (bingnet2.cc.binghamton.edu [128.226.1.18]) by hub.freebsd.org (Postfix) with ESMTP id 8EB2F1556D for ; Wed, 3 Nov 1999 11:30:11 -0800 (PST) (envelope-from zzhang@cs.binghamton.edu) Received: from sol.cs.binghamton.edu (cs1-gw.cs.binghamton.edu [128.226.171.72]) by bingnet2.cc.binghamton.edu (8.9.3/8.9.3) with SMTP id OAA07305; Wed, 3 Nov 1999 14:29:40 -0500 (EST) Date: Wed, 3 Nov 1999 13:26:30 -0500 (EST) From: Zhihui Zhang To: Matthew Dillon Cc: Greg Lehey , freebsd-hackers@FreeBSD.ORG Subject: Re: Granularity of disk I/O In-Reply-To: <199911031744.JAA59898@apollo.backplane.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > From the system's point of view, there is no difference in reliability > between doing a single sector transfer and a multi-sector transfer > except for the size of the retry. Since retries do not occur very often > nobody really cares how big the retry is. Since there is a huge > performance gain doing multi-sector transfers, that is what the > system does. > Thanks. It seems to me that for a filesystem, a block (or a fragment) is the unit of I/O. Even if a single byte is modified, an entire block probably consisting of multiple sectors must be written back to the disk. As you said, there is no differnce whether we write this block one sector at a time or in a single transfer. If so, I wonder whether the atomicity of a sector I/O required by a directory file is necessary any more. -Zhihui To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message