overview.rst

 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.. toctree::
20
21   blocks
22   blockgroup
23   special_inodes
24   allocators
25   checksums
26   bigalloc
27   inlinedata
28   eainode
29   verity
30   atomic_writes