From owner-freebsd-questions Wed Jun 13 20:15:47 2001 Delivered-To: freebsd-questions@freebsd.org Received: from dan.emsphone.com (dan.emsphone.com [199.67.51.101]) by hub.freebsd.org (Postfix) with ESMTP id 4D44B37B401 for ; Wed, 13 Jun 2001 20:15:42 -0700 (PDT) (envelope-from dan@dan.emsphone.com) Received: (from dan@localhost) by dan.emsphone.com (8.11.3/8.11.3) id f5E3FZi04113; Wed, 13 Jun 2001 22:15:35 -0500 (CDT) (envelope-from dan) Date: Wed, 13 Jun 2001 22:15:34 -0500 From: Dan Nelson To: "mail_box_of_mine@yahoo.com" Cc: freebsd-questions@FreeBSD.ORG Subject: Re: _? About SCSI request Message-ID: <20010613221534.A19081@dan.emsphone.com> References: <20010613175933.BB5F.MAIL_BOX_OF_MINE@yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20010613175933.BB5F.MAIL_BOX_OF_MINE@yahoo.com> User-Agent: Mutt/1.3.19i X-OS: FreeBSD 5.0-CURRENT Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In the last episode (Jun 13), mail_box_of_mine@yahoo.com said: > hi, > I have post this question in freebsd-questions@freebsd.org. But > no one answer me, so I have to ask freebsd-scsi@freebsd.org. Thanks in > advance. > > I have a question: If the OS (FreeBSD) submit two write request > to a SCSI driver, will the two request overlap? eg. > block = 0 size = 30 > block = 3 size = 50 > will this case happen? Only if the two writes were caused by a user doing I/O on a file opened with the O_FSYNC flag, or if the user called fsync() on the filehandle between two writes, or if the writes are on a filesystem mounted sync. Most of the time, userland write() calls are cached for a little while before being written to disk, so FreeBSD would end up writing one block, 53 units long to disk. > How about other OS? (Linux? Windows? ....) > How about IDE request? Same rules apply. Both Linux and windows have a write cache. -- Dan Nelson dnelson@emsphone.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message