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Wilson III" To: Zygo Blaxell Cc: Btrfs BTRFS References: <20201125042449.GE31381@hungrycats.org> <60820e39-5277-7d16-f3c2-bca7c3b44990@panasas.com> Message-ID: <5c7e5a89-08c2-bf61-9adc-0f4d4695bd4b@panasas.com> Date: Thu, 26 Nov 2020 09:15:34 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 In-Reply-To: <60820e39-5277-7d16-f3c2-bca7c3b44990@panasas.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [2601:41:c500:5110::c161] X-ClientProxiedBy: MN2PR02CA0018.namprd02.prod.outlook.com (2603:10b6:208:fc::31) To BYAPR08MB5109.namprd08.prod.outlook.com (2603:10b6:a03:67::33) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2601:41:c500:5110::c161] (2601:41:c500:5110::c161) by MN2PR02CA0018.namprd02.prod.outlook.com (2603:10b6:208:fc::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3611.20 via Frontend Transport; Thu, 26 Nov 2020 14:15:38 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: a3c25426-af6e-4760-6374-08d89215bfeb X-MS-TrafficTypeDiagnostic: BYAPR08MB5573: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8882; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: aJubcY/7W+G53V4/kPbBRZMrjSZY6K+u1SS1JLleHRMG7KlOgY29t84/UqMFxtW0/wlQNXvku65lyJsok4I8LYugqKjBxJRU9y+Krwo3uLi3yZZTSPmLu2B/5UiKsQV1/ZkKAa1up1zfU5NbbUHkVAmBl17ltpkTrHFV6Mv8W9Bh2sdvoFKgx7+GtD5az68fosi7rAtzliMUPH+eYrJdmx8HVR63h9lQBG0mssW1M8aC2w0bElBSQQrFGm2decjg9RowLVRdme12UvLzfOIYHx2jiu7h8ahaOHubrIkDLJBrmDsVB4+u+DafOMBIu9j+nDT6ITW/UbAJse1xyvzOxUKmQeQROiCBIbYqhtYmhbnL9d3WNNisn/yyK2WFuj3n4Z+yUuA1p45L1S8MdTF/Ew== X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR08MB5109.namprd08.prod.outlook.com;PTR:;CAT:NONE;SFS:(376002)(366004)(346002)(136003)(39840400004)(396003)(66556008)(6666004)(316002)(2906002)(4326008)(31686004)(36756003)(6486002)(2616005)(66946007)(5660300002)(186003)(53546011)(66476007)(16526019)(52116002)(8676002)(8936002)(478600001)(83380400001)(86362001)(31696002)(6916009)(14143004)(43740500002);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?dXZadkpYdlF1TkJlUHhGZzRsQ0RrU0xXTnF6bnFKd2kyRVlkY3U4ODlIaS9y?= =?utf-8?B?R0dFc291U3hHUnJvM2wvSXlBYmdQRGVQUmxGRzRhemlPdjVRTUJGWngyVFF6?= =?utf-8?B?Sm9GUy9UcXBSa3R2M0dzUE4zU1Q3YlRUTzF4akk2aXRtVEdrUGVKV0RFUnBW?= =?utf-8?B?aHJBWWpzNjhzOFBpZ1BTRFl2TlhNWFA0WkxIcDRnNVkwNUs3MFhteGl0MlAw?= =?utf-8?B?R1BZd1g1T1I0Y1ZTWllEZHRYK3BJRlVpYWlRbVIyVlVjaUNsRWJNQnFHMEZk?= =?utf-8?B?TkpoajA1cDErcUMvNXFJdFREODhTWmU1TTRLbitrUC9BUmd0VzA0Sm1oaVph?= =?utf-8?B?L1k0S3NPSUFWd25LVjlEWVYyUDhTeVY3RzJzRXQxbUQyK2JpOFpReFArZzcx?= =?utf-8?B?UHRBL21pZjhpVWorQkJ3Mmc3bmhScCtSb2IwZUd6aEY1NTJMM1pORFlGVm5H?= =?utf-8?B?cHNOQVBOWmIyM2czb0dpZGxwQ25SdmFEK0hneGdGYndTTXZxQ09VOERETkFo?= =?utf-8?B?RERsWTZLUEQvY0VVUlZOelRZY1BJNlloUEh4dHFKSlJmZFJhSElrbG9Pb0VE?= =?utf-8?B?WnJSem13R2p0QzlkcUMveUlIaVBIa2E4VE9pcCtLOVZVQnBCTU5NSkVBaUtm?= =?utf-8?B?bE9zRDdTN1FWNkxJY3VTSzVLM2lBRlZMclplRE85djIyVkNxQ2w4TzdOU3h0?= =?utf-8?B?TFpxN2o0K1JTanlwdHRtdlBGWU5JcGk3bkhGd0w2WUs3MW8xM1J6UklaNVYr?= =?utf-8?B?d2pGaWdsQ05QZDNvUUFqVGlabURZOUVHQjhYU0ZQeWlKVlFaVUNSNitVZEFL?= =?utf-8?B?ZUpLVXRCSzcvbllBcUVkVU5rSm5FbE41UVNic28rM1hiOUxVaHp6TGpldVZS?= =?utf-8?B?NXVmRGdwTktnYzhQZlF0ekl2ek44NkppMWU2dXFMOUM3bFlySVBvTDBLaWRl?= =?utf-8?B?ZVdOUm5vOTEvNUNmUmpFS2NXOG1MRy8rRlM4RVM3MVNua3FBaTNnTzZLQmts?= =?utf-8?B?QzBteS91clJzem0zV29SWXpGd1JCb2J6Ym9rVk5nQzJIeWJHNkd3ak5JY0lu?= =?utf-8?B?ajVtclN5ZlYvbGp0RkJYWkF1b2NrekV1RTIvVndHeDAyendqMjVZL0NLMkJW?= =?utf-8?B?T25FbFVDZExFVDJ1c243bWU5VktHOVhlazN1Tk1NdllVUm5TSG1kUlFXYTRj?= =?utf-8?B?d21CZXdFcTBOdHZLT1VMU1VVVmowa3hzNitKWGZBeDhKU2VZN0Q4VmxheHNZ?= =?utf-8?B?NmFaaWlNNUZzTVN0bTd5NWs2UmR4NEw1d1d5dVh0QlAzL1RKWUJ6Zzl4RDlk?= =?utf-8?B?U1V6Y21RMU5XYlgzcVRnM3BPNkY0R1FSNjRVcDR1RmhqZHJ1cG1BRmdlOWZ0?= =?utf-8?B?Y05OUVJ3MlluY3c9PQ==?= X-OriginatorOrg: panasas.com X-MS-Exchange-CrossTenant-Network-Message-Id: a3c25426-af6e-4760-6374-08d89215bfeb X-MS-Exchange-CrossTenant-AuthSource: BYAPR08MB5109.namprd08.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Nov 2020 14:15:38.7906 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: acf01c9d-c699-42af-bdbb-44bf582e60b0 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: P7xrFhFH47GJy/j/5Q8LXlaZPo/+5Yyx1kGBvDKvQAHQ9VtNSS4BhENV/VDwfULcZGyaygWcC6j0xuqhC3Bz0g== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR08MB5573 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 11/25/20 10:16 AM, Ellis H. Wilson III wrote: > On 11/24/20 11:24 PM, Zygo Blaxell wrote: >> On Tue, Nov 24, 2020 at 11:03:15AM -0500, Ellis H. Wilson III wrote: >>> 1. Is my presumption just incorrect and there is some other >>> time-consuming >>> mechanics taking place during a snapshot that would cause these >>> longer times >>> for it to return successfully? >> >> As far as I can tell, the upper limit of snapshot creation time is >> bounded >> only the size of the filesystem divided by the average write speed, i.e. >> it's possible to keep 'btrfs sub snapshot' running for as long as it >> takes >> to fill the disk. > > Ahhh.  That is extremely enlightening, and exactly what we're seeing.  I > presumed there was some form of quiescence when a snapshot was taken > such that writes that were inbound would block until it was complete, > but I couldn't reason about why it was taking SO long to get everything > flushed out.  This exactly explains it as we only block out incoming > writes to the subvolume being snapshotted -- not other volumes. One other potentially related question: How does snapshot removal impact snapshot time? If I issue a non-commit snapshot deletion (which AFAIK proceeds in the background), and then a few seconds later I take a snapshot of that same subvolume, should I expect to have to wait for the snapshot removal to be processed prior to the snapshot I just took from completing? Best, ellis