| Andrew Scull | b4b6d4a | 2019-01-02 15:54:55 +0000 | [diff] [blame] | 1 | .. SPDX-License-Identifier: GPL-2.0 |
| 2 | |
| 3 | Blocks |
| 4 | ------ |
| 5 | |
| 6 | ext4 allocates storage space in units of “blocks”. A block is a group of |
| 7 | sectors between 1KiB and 64KiB, and the number of sectors must be an |
| 8 | integral power of 2. Blocks are in turn grouped into larger units called |
| 9 | block groups. Block size is specified at mkfs time and typically is |
| 10 | 4KiB. You may experience mounting problems if block size is greater than |
| 11 | page size (i.e. 64KiB blocks on a i386 which only has 4KiB memory |
| 12 | pages). By default a filesystem can contain 2^32 blocks; if the '64bit' |
| 13 | feature is enabled, then a filesystem can have 2^64 blocks. |
| 14 | |
| 15 | For 32-bit filesystems, limits are as follows: |
| 16 | |
| 17 | .. list-table:: |
| 18 | :widths: 1 1 1 1 1 |
| 19 | :header-rows: 1 |
| 20 | |
| 21 | * - Item |
| 22 | - 1KiB |
| 23 | - 2KiB |
| 24 | - 4KiB |
| 25 | - 64KiB |
| 26 | * - Blocks |
| 27 | - 2^32 |
| 28 | - 2^32 |
| 29 | - 2^32 |
| 30 | - 2^32 |
| 31 | * - Inodes |
| 32 | - 2^32 |
| 33 | - 2^32 |
| 34 | - 2^32 |
| 35 | - 2^32 |
| 36 | * - File System Size |
| 37 | - 4TiB |
| 38 | - 8TiB |
| 39 | - 16TiB |
| 40 | - 256PiB |
| 41 | * - Blocks Per Block Group |
| 42 | - 8,192 |
| 43 | - 16,384 |
| 44 | - 32,768 |
| 45 | - 524,288 |
| 46 | * - Inodes Per Block Group |
| 47 | - 8,192 |
| 48 | - 16,384 |
| 49 | - 32,768 |
| 50 | - 524,288 |
| 51 | * - Block Group Size |
| 52 | - 8MiB |
| 53 | - 32MiB |
| 54 | - 128MiB |
| 55 | - 32GiB |
| 56 | * - Blocks Per File, Extents |
| 57 | - 2^32 |
| 58 | - 2^32 |
| 59 | - 2^32 |
| 60 | - 2^32 |
| 61 | * - Blocks Per File, Block Maps |
| 62 | - 16,843,020 |
| 63 | - 134,480,396 |
| 64 | - 1,074,791,436 |
| 65 | - 4,398,314,962,956 (really 2^32 due to field size limitations) |
| 66 | * - File Size, Extents |
| 67 | - 4TiB |
| 68 | - 8TiB |
| 69 | - 16TiB |
| 70 | - 256TiB |
| 71 | * - File Size, Block Maps |
| 72 | - 16GiB |
| 73 | - 256GiB |
| 74 | - 4TiB |
| 75 | - 256TiB |
| 76 | |
| 77 | For 64-bit filesystems, limits are as follows: |
| 78 | |
| 79 | .. list-table:: |
| 80 | :widths: 1 1 1 1 1 |
| 81 | :header-rows: 1 |
| 82 | |
| 83 | * - Item |
| 84 | - 1KiB |
| 85 | - 2KiB |
| 86 | - 4KiB |
| 87 | - 64KiB |
| 88 | * - Blocks |
| 89 | - 2^64 |
| 90 | - 2^64 |
| 91 | - 2^64 |
| 92 | - 2^64 |
| 93 | * - Inodes |
| 94 | - 2^32 |
| 95 | - 2^32 |
| 96 | - 2^32 |
| 97 | - 2^32 |
| 98 | * - File System Size |
| 99 | - 16ZiB |
| 100 | - 32ZiB |
| 101 | - 64ZiB |
| 102 | - 1YiB |
| 103 | * - Blocks Per Block Group |
| 104 | - 8,192 |
| 105 | - 16,384 |
| 106 | - 32,768 |
| 107 | - 524,288 |
| 108 | * - Inodes Per Block Group |
| 109 | - 8,192 |
| 110 | - 16,384 |
| 111 | - 32,768 |
| 112 | - 524,288 |
| 113 | * - Block Group Size |
| 114 | - 8MiB |
| 115 | - 32MiB |
| 116 | - 128MiB |
| 117 | - 32GiB |
| 118 | * - Blocks Per File, Extents |
| 119 | - 2^32 |
| 120 | - 2^32 |
| 121 | - 2^32 |
| 122 | - 2^32 |
| 123 | * - Blocks Per File, Block Maps |
| 124 | - 16,843,020 |
| 125 | - 134,480,396 |
| 126 | - 1,074,791,436 |
| 127 | - 4,398,314,962,956 (really 2^32 due to field size limitations) |
| 128 | * - File Size, Extents |
| 129 | - 4TiB |
| 130 | - 8TiB |
| 131 | - 16TiB |
| 132 | - 256TiB |
| 133 | * - File Size, Block Maps |
| 134 | - 16GiB |
| 135 | - 256GiB |
| 136 | - 4TiB |
| 137 | - 256TiB |
| 138 | |
| 139 | Note: Files not using extents (i.e. files using block maps) must be |
| 140 | placed within the first 2^32 blocks of a filesystem. Files with extents |
| 141 | must be placed within the first 2^48 blocks of a filesystem. It's not |
| 142 | clear what happens with larger filesystems. |