From: Mikhail Morfikov <mmorfikov@gmail.com>
To: linux-ext4@vger.kernel.org
Subject: Question about ext4 extents and file fragmentation
Date: Wed, 20 Mar 2019 23:44:19 +0100 [thread overview]
Message-ID: <aad2611a-9640-9ec1-108a-f67ba662c301@gmail.com> (raw)
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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: flags:
0: 0.. 32767: 34816.. 67583: 32768:
1: 32768.. 63487: 67584.. 98303: 30720:
2: 63488.. 96255: 100352.. 133119: 32768: 98304:
3: 96256.. 126975: 133120.. 163839: 30720:
4: 126976.. 159743: 165888.. 198655: 32768: 163840:
5: 159744.. 190463: 198656.. 229375: 30720:
6: 190464.. 223231: 231424.. 264191: 32768: 229376:
7: 223232.. 253951: 264192.. 294911: 30720:
8: 253952.. 286719: 296960.. 329727: 32768: 294912:
9: 286720.. 319487: 329728.. 362495: 32768:
10: 319488.. 351367: 362496.. 394375: 31880: last,eof
/bigfile: 5 extents found
1. How many fragments does this file really have? 11 or 5?
2. Should the extents 0 and 1 be treated as one fragment or two
separate ones? I know they could be one from the human
perspective, but is it really one for ext4 filesystem?
3. What does actually happen during the read in the case of
some HDD and its magnetic heads? If the head finishes reading
the whole extent (ext 0), will it be able to read the data of
the next extent (ext 1) without any delays like in the case of
raw read (for instance dd if=/dev/sda ...), or will it be
delayed because of the filesystem layer, and the head will
have to spend some time to be positioned again in order to
read the next extent?
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next reply other threads:[~2019-03-20 22:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-20 22:44 Mikhail Morfikov [this message]
2019-03-21 3:18 ` Question about ext4 extents and file fragmentation Theodore Ts'o
2019-03-21 9:29 ` Mikhail Morfikov
2019-03-21 15:05 ` Theodore Ts'o
2019-03-21 15:59 ` Mikhail Morfikov
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