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Wed, 20 Mar 2019 15:44:27 -0700 (PDT) Received: from localhost ([5.172.255.23]) by smtp.gmail.com with ESMTPSA id i24sm549739ljb.31.2019.03.20.15.44.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 20 Mar 2019 15:44:26 -0700 (PDT) To: linux-ext4@vger.kernel.org From: Mikhail Morfikov Subject: Question about ext4 extents and file fragmentation Openpgp: preference=signencrypt Autocrypt: addr=mmorfikov@gmail.com; prefer-encrypt=mutual; keydata= mQINBFKDi0gBEADqBkwR00qrGmRq2rPM8g4LMBbLbYBtZLzFXpO+GB4sq47vZ0iq6BNwfRQG JMpHo3rYCekleN7Qqbszwt18QTCP/8aMFx6g6CcfKVmdgyoRwlGPa6YSJlFOuH3JvSFyttyT gFcyfyAJrl2aSXq5bjiyND5RuoLW5mlovfgq1YBFNg6arCo4I5h0EYVvWmKv++5CFaGg3q9W GzFpFkmJiHGlg/Wu/xP4GNZJbou07z/Y51JScw5s3KOped8ltM52ZXcVCT3eUdc6g4zX9MTS agkVo5vb7TlGPuW0LTdqsUk+dXgZo3w5NipbgU1kU6P4cxKy1XHwdSpQ/2j3zMoaW0NMIeYC o24mQkO3fJiLIAgNKq+CUwZgXkKfpkYL3QJOJkn+OwjsAJmcIhbU1Dp//JPmPUZIEGE/9gE3 K7USmb2v9hoMh9VUfe/W3AS7mFwuOPwyl8IKoVPvD7X1vIGYTv4Z4sKR4yRwW7FehfeiwafU Y8Wov6nMJ+TeS1wucc+4wy/R1GoGIaUur2y/S4G40MA5hQKzRUQ2caqDxrW7tbACxsEzgWRi Dbrlpwg9FHcOi5iwQcs0pwQmhmG5Go9SszPA/oTQIsv/tBRyTZjIlDMsHD7KwhRFTXLS3PMq cQpBt62OCEty3bO7EI4Ndbhx6k2qpJulKN3/YOXiSBA0IC7SiwARAQABtDJNaWtoYWlsIE1v cmZpa292IChzZWNvbmRhcnkpIDxtbW9yZmlrb3ZAZ21haWwuY29tPokCVwQTAQoAQQIbAwIe AQIXgAULCQgHAwUVCgkICwUWAgMBAAIZARYhBOSTz1puQu0xQ1DKqc0EaBB3G2UgBQJcXUQ1 BQkLuuxtAAoJEM0EaBB3G2Ug908QAKZ9WUWLcipmHJHMqn/R108KMIzOwvDUs5UcrY6Cjd03 X1sd45VO4DdBGmi2y4v+ziO+iAQB0BaJKr3d7ILUUA/QD3NXx9HgnXI9g1MFouqf/idTy+iH Nxx36v4zwnFN9BZWsx4zjMSVSh0gZsvHvpCeFvGwNVSW2cWUR73b5lE59pNR+AALFAY1KkFc IKM2lrkcDY4xsvuT4tqBy5t3/dzrkyuAMxlZxQiPtTRTHwWh/KlF1ZCyQrdCUjhjbQfXoi+U gQu/sXjEeOeA2n7Jv9RX8ZvghGuKawxogZhvETObXBubzImI/k+iZmibZye4b1yxaQ5naQXp i5iBWwTzVJK8Os/T/ScbSgDDTZIB9dic8pcie/EzDWYUWyxEzc6/OsOFjb8N3LLqc4JUyLK/ X+xgLXvp5dQEhy24b1oXb3LuIyDhDJgzmXMqqCr3cXq0N7sxkNKGI9L6f279YiEsq9+i3bVa +kdUZtbZwQKTWOrQ/DANZ1qlA0TiXTOx+aoVCjr9w70s33eFhv740zImWQnclqC3hjxUn0iA 5AKirgm95xEKqCeEKTdSg2h1rIgj3hlE1shqRuiA9BMQdRXpNh03w40x/CrCw2L3RXcf3LWe 2XxSK3EYDptLWt0lN7R2Btz3hi/7QfU6K8k1RYaXnl63+Vybg4xLkXvzzkkcE+6duQINBFKD i0gBEADKPLX2vMQgwmAUbMDJc8jIjFrHqNOeiMLT2NpVqP4mYbsIeUsGERH6XpMeoSr3v4cs R3dw6kE+OBT5DqztyzpnPVOKENsXpcncKPhviM2DpWizfpwymDB+80vjYaNVJ272iyBFVlD/ wCfCQVF3TFgPS4suEx4+02+cZ/whP1oCasllIrSpiCLMGCLFI0Hrn4mZtZB8scZQBLhDRuT8 ebKUKGakxMuqYxWpElX6VsUUl25vGuBlnjAPdwJSK7WYhyAAYu3zTxEOafJGaRCnX5lu0td4 DFvUmWDEUYRN/xiyCanHrwK+gyCiM3D+5NRVqi4vB5xV+ZZHbyDd69m7nTRQI8IqfFfdEFms Vicfyyh8t3pwNeOs9OulMXA6heBKsgNBxSRfFewzlpkIHIMuyiyejySnAsr9wzHu5ZyfNPb1 HVfPLMRJ0WTsrPcn3xE367OrdLX8ZOCAcsJXZL7dMRLLyIARam92bLa8f9VBJbwHZRABnfgP pO/sphgyFL8I8bMWAnQQHcIYU7KuXV7lS2U23ockrl5SPr7YklFDNVgq9n+eq270AUkX14Yx aHr3tKrgVbuYlaz5BAxZvZNALit4cL5zSOwDTeegYZlV4DXXoS6SFJzv+E4jZ6iYC8X8Im6Q s/Rqjsi6TVMYE4vV+hdBEFzTSJM3da2WKiDqpaNI4QARAQABiQI8BBgBCgAmAhsMFiEE5JPP Wm5C7TFDUMqpzQRoEHcbZSAFAlxdRJsFCQu67NMACgkQzQRoEHcbZSBlKw//TYPt68ZkcSV/ vjim+QvsTLOLtY1hzB5zIlz7viIOlBuTl6btI/QDPxE2HxgiIi1g+inB32p3uJQzfYpTvK+Y c8ItwiPXhIwdTWNhlzS1iXoVQdj9jJUlM2Y91KtratRtAQcwgWOSe2pl1KrQoVctBwRE4Bbs PONiJlaaEyjZIrdfGcj1dURm0C0iLkEG/Le1VvQxS9mKWnoIWnxTyle5cN44a06hUmDWVuqX l3uQr9E4mRvxVkAN4dItftVhpeCe0oZcxDGKFiBguRD2SCq0h/gQfQGUyApo1KsrH9C7ny+Z tOvUHCEIM9PlGmqA8lFVj+P5gbcUfW5Duqu0D5NPWLGhIfLSCxg8LGFd9GPC2UxYt4aCuS02 0MKhEHsHfg7c2avqfQ9xK0l8ZrROax0gdniz2lPkSdB+S6Z9XqamgGbZnXYU1dJaM2r35tOd YfVgG9nf7g2bxCa9wmYdBR2ZDri5o6Pwd76xAp5J5W9GCfiY0uH5qfy4899JxLNgEx7PheZ6 0x69Z+hTiaMv3+9mY24G/KmwnOnYDp/0lVdTczGzozD9xYaG4ReP/gS2TQMKwEto8IEX336C Bj+Sti8AiDaBCrnhCERxAbYwJTbtTP05fg5u/JorJfD6L76A2wHn9il1yJ4/HAJgs7KGevUg VyIzwTcJuLgTKoPQBcfsUkg= Message-ID: Date: Wed, 20 Mar 2019 23:44:19 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="bT9jIS82RJb0WArOv5q7mJ7aNdmlagQq4" Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --bT9jIS82RJb0WArOv5q7mJ7aNdmlagQq4 Content-Type: multipart/mixed; boundary="kAGSEFb9zHjWpJRdlyqixx21AOGHpBYwc"; protected-headers="v1" From: Mikhail Morfikov To: linux-ext4@vger.kernel.org Message-ID: Subject: Question about ext4 extents and file fragmentation --kAGSEFb9zHjWpJRdlyqixx21AOGHpBYwc Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable When we have a big file on an ext4 partition, and filefrag shows the following: filefrag -ve /bigfile Filesystem type is: ef53 File size of /bigfile is 1439201280 (351368 blocks of 4096 bytes) ext: logical_offset: physical_offset: length: expected: fla= gs: 0: 0.. 32767: 34816.. 67583: 32768: =20 1: 32768.. 63487: 67584.. 98303: 30720: =20 2: 63488.. 96255: 100352.. 133119: 32768: 98304: 3: 96256.. 126975: 133120.. 163839: 30720: =20 4: 126976.. 159743: 165888.. 198655: 32768: 163840: 5: 159744.. 190463: 198656.. 229375: 30720: =20 6: 190464.. 223231: 231424.. 264191: 32768: 229376: 7: 223232.. 253951: 264192.. 294911: 30720: =20 8: 253952.. 286719: 296960.. 329727: 32768: 294912: 9: 286720.. 319487: 329728.. 362495: 32768: =20 10: 319488.. 351367: 362496.. 394375: 31880: las= t,eof /bigfile: 5 extents found 1. How many fragments does this file really have? 11 or 5?=20 2. Should the extents 0 and 1 be treated as one fragment or two=20 separate ones? I know they could be one from the human=20 perspective, but is it really one for ext4 filesystem? 3. What does actually happen during the read in the case of=20 some HDD and its magnetic heads? If the head finishes reading=20 the whole extent (ext 0), will it be able to read the data of=20 the next extent (ext 1) without any delays like in the case of raw read (for instance dd if=3D/dev/sda ...), or will it be=20 delayed because of the filesystem layer, and the head will=20 have to spend some time to be positioned again in order to=20 read the next extent? --kAGSEFb9zHjWpJRdlyqixx21AOGHpBYwc-- --bT9jIS82RJb0WArOv5q7mJ7aNdmlagQq4 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEE5JPPWm5C7TFDUMqpzQRoEHcbZSAFAlySwkkACgkQzQRoEHcb ZSDtMxAA3p05Wbi24G/17i3OsZbzLarLrzPZSEJU/wgKbE/0jb1Uv0wBYyr8jDhB /AjvIv3wRS3C4Nng6rnspIkosmK6yaGvgEjKxkCsRL3sfkNaeso6pI/u8m0RDxsv zoniM3+QWZ0J1nT3Dft0AQpZv5lV7LDboyXaFZlnF4AvceDa8HXqSmM5patl8SvL GnzzyOE3xGNRE5x67Hftw3jFXqS4s9XJdvxpTobtnAoz1EAx1V2UR2WY3D/oWK2X ZeqlkaS3Zy3RE2iHYbhhPwkn54ANgBWk+boPYUKLhPw6z7s2gIKl1K1WjO5g4VPR IGXtVS2NfMQuJXDuIJH4UIwEw4YznkYyQoRzrbRGNzLd6f5cOpRJvwcdZ4vukQmD 9E06Fw6ssdQgfZrsYfsfxAJOyoQp5q9wfal34bNswObFHvxIc58R6frmFOlBpnVl gZIOcS9Aldn0X4FrH/NIugDomobwQynlO0DQbwVogY1LGGxw/tovfe5H2LnEvNs7 +m7GSl5YKun399FiU7csa2S1Evw0GPvkpDn4rkuGJzjgtnTRqes4bfs42E0WiuaK jJbU9yUgo7QVlnVphv2PFm5noLQ0zcEaf4FbktDRwUaBrvMHIakSZ9907ILu6ZiJ gjXJ2RqK4rYj69CjehlY3327hnuMvmuUXYa4Q+RZvGmVahkGjB8= =6U+G -----END PGP SIGNATURE----- --bT9jIS82RJb0WArOv5q7mJ7aNdmlagQq4--