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1 .. SPDX-License-Identifier: GPL-2.0
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7 generally a desirably quality of a filesystem. On a spinning disk,
9 that the head actuator and disk must perform to access a data block,
13 effect of concentrating writes on a single erase block, which can speed
17 The first tool that ext4 uses to combat fragmentation is the multi-block
18 allocator. When a file is first created, the block allocator
23 files) then the file data gets written out in a single multi-block
24 extent. A second related trick that ext4 uses is delayed allocation.
25 Under this scheme, when a file needs more blocks to absorb file writes,
27 the dirty buffers are being written out to disk. By not committing to a
32 The third trick that ext4 (and ext3) uses is that it tries to keep a
34 on the seek penalty when the filesystem first has to read a file's inode
35 to learn where the file's data blocks live and then seek over to the
38 The fourth trick is that all the inodes in a directory are placed in the
40 here is that all the files in a directory might be related, therefore it
41 is useful to try to keep them all together.
44 groups; these mini-containers are used as outlined above to try to
45 maintain data locality. However, there is a deliberate quirk -- when a
49 over a disk; as the top-level directory/file blobs fill up one block
53 the end of a spinning drive get a raw deal performance-wise.