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[76.167.209.94]) by smtp.gmail.com with ESMTPSA id 82sm5230617pfv.214.2020.05.09.14.01.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 09 May 2020 14:01:35 -0700 (PDT) To: Zygo Blaxell , Rich Rauenzahn Cc: Btrfs BTRFS References: <20200504230857.GQ10769@hungrycats.org> From: Phil Karn Autocrypt: addr=karn@ka9q.net; keydata= mQENBEw2mJ4BCADELiPsLFHDwapoSU7d2xNHxmwzzrFUCZWhO34kM6G5+o9GUNmGgMQ0BmXp I6hx77HHnrj9FC6kWh/bxBt3+o8HW+NTWzJSvf6kW7ThaNt7v9iewkS23JOMarAZs4qy6MhT 1RW1/yWY7RimWxrmkKPTKKa0Ad4CWT6fcP3t+doqGslSQIeoTh0C33ZT+LY59Wcr224iXohN 4Uu/nFe4yAHjtA+4Sesveo3Tyi8cbOgkcO6vij+pXesCcuhtGMlnE2dxRqbenrfVGLUVxNug LkQdLWezaGGm+dcjWYk1xjtaDnsCpVaYCMsfYNADQPJAjAFu37pVdoXhseVXfzOUN2EXABEB AAG0GVBoaWwgS2FybiA8a2FybkBrYTlxLm5ldD6JATgEEwECACIFAkw2mJ4CGwMGCwkIBwMC BhUIAgkKCwQWAgMBAh4BAheAAAoJEPFOQ1TtRjRGU98H/Atsb/N4lNbzNdzdIRcHD9XgCEa1 UdR4mxgjwvLxS1nYRNdHwfTxvA5nxWfMx/0CB26VaNFdI3lkg/S0vYsSUu6M7l8Zb8v4JMyU 4B4yvkFHZ3II5oilzIMa3e2cMfDz7TSwO1JcXyI5y9vHnvH65/LQF+QojDgzf3vXKiNdTXJp 3nEa5IgMAB0rcSNsXFx8xbHi8s5niL9+1I7XTPvVMeXrMe8h4AG1nM/dK96WwmV+tLyXKYXn xVeb9F4X9CNQbkn/xAH+egvKHHT3V7K9cAhrDfu9Qwpo7zKk/akBpLWG2kmkTOfhXjm3UQhv MVgDmpeQIYa1HgAsKrsDQMzrIFm5AQ0ETDaYngEIAJmFdm0MmENzLEosD1FvGPJleWDYb0ah 8dOk4XUug1RhW40f7AsugT75pKs9PolXt92920GdU727X3Jpgdj4kLDtIQA0KZrOXiEOZjIZ WcROAyvTGyMs/P7Um1AGNM161Ga6/Wtlc076FN7EUQtzPbthH26M3lGWUX0Ccls/8Ep4qbnF IrMRBxjaxKbqfKPTeU10pDykzA7s5hiNe7qaegvqD6YLseZ+6FqCn988YnLiIaFeNbWxUY5G spjAsfesnAmpn5vhUqAGiizkNlAMIN31xvpLd93oM4/vORszIuN1UP2RlxL3s30BncZl2XOd Mk1/59Sy70zVqF1ANyMrA18AEQEAAYkBHwQYAQIACQUCTDaYngIbDAAKCRDxTkNU7UY0Rszt B/9ZPH9xw47lPkVJRbhgf0G7fdsxsyiuouAqOKklUNFSy4+qeGomjwE6YvdMybwGtaUGla7t 2mDzrva+7Gzb0inXIgmahQPmM16F3GVxGoFL+QJ+7gD8Hco6e0/2kju7ZREDE7SOEwKb3lhD eNLccfX2AqAHfCT/LVLbgBpMRmwUJQThM+33Z2L9BqIM3awj2mOTmeDumpxiDfroU90mGc9c pXe4YrNIkL/N8eMzLe1bpu+mpPCiIrEO+dFA7N8jjVcOCQ4Lr8sU6cOsEdkaACZiNFKT99eb NkKigK8sEkDZc/AKhPCEsnaZpwBZPScOL88LLi7FHj9Osznt+uhWfbLe Subject: Re: Western Digital Red's SMR and btrfs? Message-ID: Date: Sat, 9 May 2020 14:00:16 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200504230857.GQ10769@hungrycats.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 5/4/20 16:08, Zygo Blaxell wrote: > The basic problem with DM-SMR drives is that they cache writes in CMR > zones for a while, but they need significant idle periods (no read or > write commands from the host) to move the data back to SMR zones, or > they run out of CMR space and throttle writes from the host. Does anybody know where the drive keeps all that metadata? On rotating disk, or in flash somewhere? Just wondering what happens when power suddenly fails during these rewrite operations. > > Some kinds of RAID rebuild don't provide sufficient idle time to comple= te > the CMR-to-SMR writeback, so the host gets throttled. If the drive slo= ws My understanding is that large sequential writes can go directly to the SMR areas, which is an argument for a more conventional RAID array. How hard does btrfs try to do large sequential writes?