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Thu, 11 Feb 2021 15:26:04 +0000 From: Johannes Thumshirn To: "dsterba@suse.cz" CC: Naohiro Aota , "linux-btrfs@vger.kernel.org" , "dsterba@suse.com" , "hare@suse.com" , "linux-fsdevel@vger.kernel.org" Subject: Re: [PATCH v15 00/42] btrfs: zoned block device support Thread-Topic: [PATCH v15 00/42] btrfs: zoned block device support Thread-Index: AQHW+uBDi/qAxtbkv0uUNvQXEiNsGQ== Date: Thu, 11 Feb 2021 15:26:04 +0000 Message-ID: References: <20210210195829.GW1993@twin.jikos.cz> <20210211151901.GD1993@twin.jikos.cz> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: suse.cz; dkim=none (message not signed) header.d=none;suse.cz; dmarc=none action=none header.from=wdc.com; x-originating-ip: [129.253.240.72] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 7811aa06-ded8-4072-d314-08d8cea1587a x-ms-traffictypediagnostic: SN6PR04MB3807: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:8273; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SN4PR0401MB3598.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 7811aa06-ded8-4072-d314-08d8cea1587a X-MS-Exchange-CrossTenant-originalarrivaltime: 11 Feb 2021 15:26:04.1316 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 0RQmHPrFB4QGhDYV88qEzvk/+8izT3PolwysnzRq0jA/dy4RMi0+p19OICHjx7UXFAX94Eri+vp1+P6MiFNe8d7sy6x2OWPioAQzI4VZDR4= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR04MB3807 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 11/02/2021 16:21, David Sterba wrote:=0A= > On Thu, Feb 11, 2021 at 09:58:09AM +0000, Johannes Thumshirn wrote:=0A= >> On 10/02/2021 21:02, David Sterba wrote:=0A= >>>> This series implements superblock log writing. It uses two zones as a= =0A= >>>> circular buffer to write updated superblocks. Once the first zone is f= illed=0A= >>>> up, start writing into the second zone. The first zone will be reset o= nce=0A= >>>> both zones are filled. We can determine the postion of the latest=0A= >>>> superblock by reading the write pointer information from a device.=0A= >>>=0A= >>> About that, in this patchset it's still leaving superblock at the fixed= =0A= >>> zone number while we want it at a fixed location, spanning 2 zones=0A= >>> regardless of their size.=0A= >>=0A= >> We'll always need 2 zones or otherwise we won't be powercut safe.=0A= > =0A= > Yes we do, that hasn't changed.=0A= > =0A= =0A= OK that I don't understand, with the log structured superblocks on a zoned= =0A= filesystem, we're writing a new superblock until the 1st zone is filled.=0A= Then we advance to the second zone. As soon as we wrote a superblock to=0A= the second zone we can reset the first.=0A= If we only use one zone, we would need to write until it's end, reset and= =0A= start writing again from the beginning. But if a powercut happens between= =0A= reset and first write after the reset, we end up with no superblock.=0A=