LXR linux/Documentation/filesystems/ext4/blocks.rst

   1.. SPDX-License-Identifier: GPL-2.0
   2
   3Blocks
   4------
   5
   6ext4 allocates storage space in units of “blocks”. A block is a group of
   7sectors between 1KiB and 64KiB, and the number of sectors must be an
   8integral power of 2. Blocks are in turn grouped into larger units called
   9block groups. Block size is specified at mkfs time and typically is
  104KiB. You may experience mounting problems if block size is greater than
  11page size (i.e. 64KiB blocks on a i386 which only has 4KiB memory
  12pages). By default a filesystem can contain 2^32 blocks; if the '64bit'
  13feature is enabled, then a filesystem can have 2^64 blocks. The location
  14of structures is stored in terms of the block number the structure lives
  15in and not the absolute offset on disk.
  16
  17For 32-bit filesystems, limits are as follows:
  18
  19.. list-table::
  20   :widths: 1 1 1 1 1
  21   :header-rows: 1
  22
  23   * - Item
  24     - 1KiB
  25     - 2KiB
  26     - 4KiB
  27     - 64KiB
  28   * - Blocks
  29     - 2^32
  30     - 2^32
  31     - 2^32
  32     - 2^32
  33   * - Inodes
  34     - 2^32
  35     - 2^32
  36     - 2^32
  37     - 2^32
  38   * - File System Size
  39     - 4TiB
  40     - 8TiB
  41     - 16TiB
  42     - 256PiB
  43   * - Blocks Per Block Group
  44     - 8,192
  45     - 16,384
  46     - 32,768
  47     - 524,288
  48   * - Inodes Per Block Group
  49     - 8,192
  50     - 16,384
  51     - 32,768
  52     - 524,288
  53   * - Block Group Size
  54     - 8MiB
  55     - 32MiB
  56     - 128MiB
  57     - 32GiB
  58   * - Blocks Per File, Extents
  59     - 2^32
  60     - 2^32
  61     - 2^32
  62     - 2^32
  63   * - Blocks Per File, Block Maps
  64     - 16,843,020
  65     - 134,480,396
  66     - 1,074,791,436
  67     - 4,398,314,962,956 (really 2^32 due to field size limitations)
  68   * - File Size, Extents
  69     - 4TiB
  70     - 8TiB
  71     - 16TiB
  72     - 256TiB
  73   * - File Size, Block Maps
  74     - 16GiB
  75     - 256GiB
  76     - 4TiB
  77     - 256TiB
  78
  79For 64-bit filesystems, limits are as follows:
  80
  81.. list-table::
  82   :widths: 1 1 1 1 1
  83   :header-rows: 1
  84
  85   * - Item
  86     - 1KiB
  87     - 2KiB
  88     - 4KiB
  89     - 64KiB
  90   * - Blocks
  91     - 2^64
  92     - 2^64
  93     - 2^64
  94     - 2^64
  95   * - Inodes
  96     - 2^32
  97     - 2^32
  98     - 2^32
  99     - 2^32
 100   * - File System Size
 101     - 16ZiB
 102     - 32ZiB
 103     - 64ZiB
 104     - 1YiB
 105   * - Blocks Per Block Group
 106     - 8,192
 107     - 16,384
 108     - 32,768
 109     - 524,288
 110   * - Inodes Per Block Group
 111     - 8,192
 112     - 16,384
 113     - 32,768
 114     - 524,288
 115   * - Block Group Size
 116     - 8MiB
 117     - 32MiB
 118     - 128MiB
 119     - 32GiB
 120   * - Blocks Per File, Extents
 121     - 2^32
 122     - 2^32
 123     - 2^32
 124     - 2^32
 125   * - Blocks Per File, Block Maps
 126     - 16,843,020
 127     - 134,480,396
 128     - 1,074,791,436
 129     - 4,398,314,962,956 (really 2^32 due to field size limitations)
 130   * - File Size, Extents
 131     - 4TiB
 132     - 8TiB
 133     - 16TiB
 134     - 256TiB
 135   * - File Size, Block Maps
 136     - 16GiB
 137     - 256GiB
 138     - 4TiB
 139     - 256TiB
 140
 141Note: Files not using extents (i.e. files using block maps) must be
 142placed within the first 2^32 blocks of a filesystem. Files with extents
 143must be placed within the first 2^48 blocks of a filesystem. It's not
 144clear what happens with larger filesystems.
 145