Lines Matching full:block
6 The layout of a standard block group is approximately as follows (each
14 - ext4 Super Block
17 - Data Block Bitmap
22 - 1 block
25 - 1 block
26 - 1 block
30 For the special case of block group 0, the first 1024 bytes are unused,
32 The superblock will start at offset 1024 bytes, whichever block that
33 happens to be (usually 0). However, if for some reason the block size =
34 1024, then block 0 is marked in use and the superblock goes in block 1.
35 For all other block groups, there is no padding.
38 descriptors that are found in block group 0. Redundant copies of the
39 superblock and group descriptors are written to some of the block groups
41 not all block groups necessarily host a redundant copy (see following
43 copy, the block group begins with the data block bitmap. Note also that
45 GDT block” space after the block group descriptors and before the start
46 of the block bitmaps to allow for future expansion of the filesystem. By
54 As for the ordering of items in a block group, it is generally
55 established that the super block and the group descriptor table, if
56 present, will be at the beginning of the block group. The bitmaps and
60 block maps, extent tree blocks, and extended attributes.
62 Flexible Block Groups
65 Starting in ext4, there is a new feature called flexible block groups
66 (flex\_bg). In a flex\_bg, several block groups are tied together as one
67 logical block group; the bitmap spaces and the inode table space in the
68 first block group of the flex\_bg are expanded to include the bitmaps
69 and inode tables of all other block groups in the flex\_bg. For example,
71 superblock, group descriptors, data block bitmaps for groups 0-3, inode
74 block group metadata close together for faster loading, and to enable
76 and group descriptors are always at the beginning of block groups, even
77 if flex\_bg is enabled. The number of block groups that make up a
80 Meta Block Groups
83 Without the option META\_BG, for safety concerns, all block group
84 descriptors copies are kept in the first block group. Given the default
85 128MiB(2^27 bytes) block group size and 64-byte group descriptors, ext4
86 can have at most 2^27/64 = 2^21 block groups. This limits the entire
92 groups. Each metablock group is a cluster of block groups whose group
93 descriptor structures can be stored in a single disk block. For ext4
94 filesystems with 4 KB block size, a single metablock group partition
95 includes 64 block groups, or 8 GiB of disk space. The metablock group
97 first block group of the whole filesystem into the first group of each
99 each metablock group. This increases the 2^21 maximum block groups limit
103 the superblock is followed by a variable-length set of block group
104 descriptors. Instead, the superblock and a single block group descriptor
105 block is placed at the beginning of the first, second, and last block
106 groups in a meta-block group. A meta-block group is a collection of
107 block groups which can be described by a single block group descriptor
108 block. Since the size of the block group descriptor structure is 32
109 bytes, a meta-block group contains 32 block groups for filesystems with
110 a 1KB block size, and 128 block groups for filesystems with a 4KB
111 blocksize. Filesystems can either be created using this new block group
114 block group using this new layout.
117 block and inode bitmaps.
119 Lazy Block Group Initialization
122 A new feature for ext4 are three block group descriptor flags that
123 enable mkfs to skip initializing other parts of the block group
124 metadata. Specifically, the INODE\_UNINIT and BLOCK\_UNINIT flags mean
125 that the inode and block bitmaps for that group can be calculated and
127 generally the case for an empty block group or a block group containing
128 only fixed-location block group metadata. The INODE\_ZEROED flag means