| .. SPDX-License-Identifier: GPL-2.0 |
| |
| High Level Design |
| ================= |
| |
| An ext4 file system is split into a series of block groups. To reduce |
| performance difficulties due to fragmentation, the block allocator tries |
| very hard to keep each file's blocks within the same group, thereby |
| reducing seek times. The size of a block group is specified in |
| ``sb.s_blocks_per_group`` blocks, though it can also calculated as 8 * |
| ``block_size_in_bytes``. With the default block size of 4KiB, each group |
| will contain 32,768 blocks, for a length of 128MiB. The number of block |
| groups is the size of the device divided by the size of a block group. |
| |
| All fields in ext4 are written to disk in little-endian order. HOWEVER, |
| all fields in jbd2 (the journal) are written to disk in big-endian |
| order. |
| |
| .. include:: blocks.rst |
| .. include:: blockgroup.rst |
| .. include:: special_inodes.rst |
| .. include:: allocators.rst |
| .. include:: checksums.rst |
| .. include:: bigalloc.rst |
| .. include:: inlinedata.rst |
| .. include:: eainode.rst |
| .. include:: verity.rst |
