1 .. SPDX-License-Identifier: GPL-2.0 2 3 High Level Design 4 ================= 5 6 An ext4 file system is split into a series of block groups. To reduce 7 performance difficulties due to fragmentation, the block allocator tries 8 very hard to keep each file's blocks within the same group, thereby 9 reducing 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 12 will contain 32,768 blocks, for a length of 128MiB. The number of block 13 groups is the size of the device divided by the size of a block group. 14 15 All fields in ext4 are written to disk in little-endian order. HOWEVER, 16 all fields in jbd2 (the journal) are written to disk in big-endian 17 order. 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
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