Date: Wed, 3 Nov 1999 13:26:30 -0500 (EST) From: Zhihui Zhang <zzhang@cs.binghamton.edu> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Greg Lehey <grog@lemis.com>, freebsd-hackers@FreeBSD.ORG Subject: Re: Granularity of disk I/O Message-ID: <Pine.GSO.3.96.991103125823.19385D-100000@sol.cs.binghamton.edu> In-Reply-To: <199911031744.JAA59898@apollo.backplane.com>
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> 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
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