linux/Documentation/filesystems/ext4/overview.rst
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   1.. SPDX-License-Identifier: GPL-2.0
   2
   3High Level Design
   4=================
   5
   6An ext4 file system is split into a series of block groups. To reduce
   7performance difficulties due to fragmentation, the block allocator tries
   8very hard to keep each file's blocks within the same group, thereby
   9reducing seek times. The size of a block group is specified in
  10``sb.s_blocks_per_group`` blocks, though it can also calculated as 8 \*
  11``block_size_in_bytes``. With the default block size of 4KiB, each group
  12will contain 32,768 blocks, for a length of 128MiB. The number of block
  13groups is the size of the device divided by the size of a block group.
  14
  15All fields in ext4 are written to disk in little-endian order. HOWEVER,
  16all fields in jbd2 (the journal) are written to disk in big-endian
  17order.
  18
  19.. include:: blocks.rst
  20.. include:: blockgroup.rst
  21.. include:: special_inodes.rst
  22.. include:: allocators.rst
  23.. include:: checksums.rst
  24.. include:: bigalloc.rst
  25.. include:: inlinedata.rst
  26.. include:: eainode.rst
  27.. include:: verity.rst
  28