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id 15.0.1497.2; Tue, 17 May 2022 09:00:39 +0100 Message-ID: <8fc4e862-fa89-2d8d-b340-27a6465b59ca@samsung.com> Date: Tue, 17 May 2022 10:00:38 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [PATCH v4 08/13] btrfs:zoned: make sb for npo2 zone devices align with sb log offsets Content-Language: en-US To: Johannes Thumshirn , "axboe@kernel.dk" , "damien.lemoal@opensource.wdc.com" , "pankydev8@gmail.com" , "dsterba@suse.com" , "hch@lst.de" CC: "linux-nvme@lists.infradead.org" , "linux-fsdevel@vger.kernel.org" , "linux-btrfs@vger.kernel.org" , "jiangbo.365@bytedance.com" , "linux-block@vger.kernel.org" , "gost.dev@samsung.com" , "linux-kernel@vger.kernel.org" , "dm-devel@redhat.com" From: Pankaj Raghav In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [106.210.248.7] X-ClientProxiedBy: CAMSVWEXC01.scsc.local (2002:6a01:e347::6a01:e347) To CAMSVWEXC01.scsc.local 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sfid-20220517_010046_966256_336D408E X-CRM114-Status: GOOD ( 15.19 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 2022-05-17 08:50, Johannes Thumshirn wrote: > On 16/05/2022 18:55, Pankaj Raghav wrote: >> Superblocks for zoned devices are fixed as 2 zones at 0, 512GB and 4TB. >> These are fixed at these locations so that recovery tools can reliably >> retrieve the superblocks even if one of the mirror gets corrupted. >> >> power of 2 zone sizes align at these offsets irrespective of their >> value but non power of 2 zone sizes will not align. >> >> To make sure the first zone at mirror 1 and mirror 2 align, write zero >> operation is performed to move the write pointer of the first zone to >> the expected offset. This operation is performed only after a zone reset >> of the first zone, i.e., when the second zone that contains the sb is FULL. > > Hi Pankaj, stupid question. Npo2 devices still have a zone size being a > multiple of 4k don't they? > > If not, we'd need to also have a tail padding of the superblock zones, in order > to move the WP of these zones to the end, so the sb-log states match up. Hi Johannes, NPO2 zoned devices has a minimum alignment requirement of 1MB. See commit: `btrfs: zoned: relax the alignment constraint for zoned devices` It will naturally align to 4k. So I don't think we need special handling there with tail padding.