Date: Sun, 4 Aug 2002 22:43:25 -0700 (PDT) From: Lamont Granquist <lamont@scriptkiddie.org> To: "Justin T. Gibbs" <gibbs@scsiguy.com> Cc: Zhihui Zhang <zzhang@cs.binghamton.edu>, <freebsd-hackers@FreeBSD.ORG>, <freebsd-scsi@FreeBSD.ORG> Subject: Re: transaction ordering in SCSI subsystem Message-ID: <20020804223605.X892-100000@coredump.scriptkiddie.org> In-Reply-To: <200208042111.g74LBVSY063691@aslan.scsiguy.com>
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So what exactly gets ordered and how do things get tagged? I tried following this in the code from VOP_STRATEGY and never quite figured it out. Basically when you do a write are you just tagging the data writes along with the metadata writes and then sequencing them so that they have to complete in a given order? And can operations with different tags be mixed around randomly? Also, how does the feedback from the SCSI controller that the write completed get used by the O/S (and the corollary being how does IDE write caching lying about completion affect the O/S and the data integrity)? On Sun, 4 Aug 2002, Justin T. Gibbs wrote: > >While reading the document on FreeBSD SCSI subsystem, I am wondering what > >does guaranteed transaction ordering mean? Does it have anything to do > >with I/O ordering, tagging, write caching, etc.? > > Yes, yes, and yes. CAM guarantees that transactions are queued to > the device in the order they were queued to CAM. Even if an error > recovery action occurs, I/O is retried/resumed in order once the > device is recovered. > > -- > Justin > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message > > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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