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Thu, 11 Feb 2021 12:54:31 -0500 (EST) Date: Thu, 11 Feb 2021 18:54:29 +0100 From: Klaus Jensen To: Keith Busch Subject: Re: [PATCH 2/2] hw/block/nvme: add write uncorrectable command Message-ID: References: <20210210070646.730110-1-its@irrelevant.dk> <20210210070646.730110-3-its@irrelevant.dk> <20210211033732.GE23363@redsun51.ssa.fujisawa.hgst.com> <20210211153754.GC28207@redsun51.ssa.fujisawa.hgst.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="4jVbPjVgXtoysTS8" Content-Disposition: inline In-Reply-To: <20210211153754.GC28207@redsun51.ssa.fujisawa.hgst.com> Received-SPF: pass client-ip=66.111.4.28; envelope-from=its@irrelevant.dk; helo=out4-smtp.messagingengine.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , qemu-block@nongnu.org, Klaus Jensen , Gollu Appalanaidu , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --4jVbPjVgXtoysTS8 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Feb 12 00:37, Keith Busch wrote: > On Thu, Feb 11, 2021 at 09:43:05AM +0100, Klaus Jensen wrote: > > On Feb 11 12:37, Keith Busch wrote: > >=20 > > > Is there a use case with a real qemu guest wanting this? > >=20 > > Like for the extended metadata case (which also does not have a lot of > > "public" exposure, but definitely have enterprise use), our main > > motivation here was to ease testing for compliance suites and frameworks > > like SPDK.=20 >=20 > I'm okay with the metadata patches. >=20 > > I'm honestly have no clue what so ever what a real world use > > of Write Uncorrectable would be. It's been in the spec since 1.0, so > > there must have been some reason, Is it just to align with SCSI WRITE > > LONG? I'm not SCSI expert at all, but from what I can read it looks like > > that was also intended as a feature for testing read error conditions. >=20 > I don't think it's for testing purposes. >=20 > If you need to send a burst of non-atomic writes (ex: writing a RAID > stripe), a power failure can result in an inconsistent state where you > don't know at a block level which ones have old data or new data. If you > Write Uncorrectable first, you can never read old data, and thus have no > "write hole". >=20 > Journalling solves this better, and I'm not aware of any real > implementation relying on uncorrectable. Right, thanks! I'm aware of the RAID write hole issue, but I did not consider Write Uncorrectable as a possible means to solve it. --4jVbPjVgXtoysTS8 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEUigzqnXi3OaiR2bATeGvMW1PDekFAmAlb1MACgkQTeGvMW1P DelLmQf+JAmpiBLlagKOmklLkE3te5+NqI/0+ZZDo963DnrSusz0bP7zlGRVLp1I NkJSUzA9mQ2AV3q60s0c8OV+i/1ZSiXFuZL5rawbxxnxe4WvXZafJ8ZYqsPOxRDL jaPo5f22gSXATLaWKt80Op2aszlfo0BcetyeOupByzOQmq3SbBRnNH5mWVHh0qHA KNdJCzeKPElLxMDt5vB3oqOjVoCKTvtQyq2GJuXM8YeMHpygmG4gFxAqnW4449Al dbxu6p5ygl2ToL/SZDIJSYQ78TMNFbpfTOvOaJ2dq2dK1UHbYNovT0I3WlpDVajW xcnAm5p7VXIaBlN0Uda0nUXH3GrG9g== =Pn6p -----END PGP SIGNATURE----- --4jVbPjVgXtoysTS8--