From owner-cvs-all Wed Dec 8 6:47: 5 1999 Delivered-To: cvs-all@freebsd.org Received: from mojave.sitaranetworks.com (mojave.sitaranetworks.com [199.103.141.157]) by hub.freebsd.org (Postfix) with ESMTP id C334B14BDC; Wed, 8 Dec 1999 06:46:59 -0800 (PST) (envelope-from grog@mojave.sitaranetworks.com) Message-ID: <19991207210139.51228@mojave.sitaranetworks.com> Date: Tue, 7 Dec 1999 21:01:39 -0500 From: Greg Lehey To: Julian Elischer , Matthew Dillon Cc: Mike Smith , cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG Subject: Re: cvs commit: src/sys/kern kern_shutdown.c Reply-To: Greg Lehey References: <199912070829.AAA75674@apollo.backplane.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: ; from Julian Elischer on Tue, Dec 07, 1999 at 01:11:41AM -0800 Sender: owner-cvs-all@FreeBSD.ORG Precedence: bulk On Tuesday, 7 December 1999 at 1:11:41 -0800, Julian Elischer wrote: > > On Tue, 7 Dec 1999, Matthew Dillon wrote: >> >> The disk can lie about whether it has written data to the disk without >> messing softupdates up, but it cannot reorder writes that the system has >> told it must be ordered. SCSI has a tag to guarentee ordering (or not), >> but I don't know if IDE has the same sort of feature. > > Softupdates ensures the ordering by not isuing a dependent write until > it is told that the dependency write has completed. > > Thus, if the drive says a block is written but it is really in cache, and > the system issues another write that depended on the first, the second > must not be able to 'overtake' the first. THe safest way to guarantee this > is to just not allow the situation to occur. Even this is not enough for Vinum. Take one drive with a long request queue and another with no queue at all. Issue a command to the first drive, get the data into cache and issue the command to the second drive. The second drive writes immediately, before the first, then you have a power failure. Bang goes your order. Greg -- Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message