From 8a98ec7c7b3901330a036af0f62f523c31d763da Mon Sep 17 00:00:00 2001 From: "Darrick J. Wong" Date: Fri, 5 Oct 2018 19:20:08 -0400 Subject: docs: promote the ext4 data structures book to top level Move the ext4 data structures book to Documentation/filesystems/ext4/ since the administrative information moved elsewhere. Signed-off-by: Darrick J. Wong Signed-off-by: Theodore Ts'o --- Documentation/filesystems/ext4/overview.rst | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) create mode 100644 Documentation/filesystems/ext4/overview.rst (limited to 'Documentation/filesystems/ext4/overview.rst') diff --git a/Documentation/filesystems/ext4/overview.rst b/Documentation/filesystems/ext4/overview.rst new file mode 100644 index 000000000000..cbab18baba12 --- /dev/null +++ b/Documentation/filesystems/ext4/overview.rst @@ -0,0 +1,26 @@ +.. 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 -- cgit v1.2.3