ext2文件系统 - mke2fs
2018-02-13 20:32
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上一遍博文的重点其实将ext2整体的组织框架,我们知道了ext2文件系统由块组组成,每个块组里面的组织形式。我们甚至直接把超级块和组描述符里面的内容,用十六进制形式展现了出来。这篇博文主要讲述如何mke2fs生成合适需要的ext2 文件系统,基本就是参数选择的问题。
mke2fs 常用的几个参数有:
1) -b block-size .
块大小是ext2文件系统比较重要的一个参数,目前只支持1024、2048和4096。上篇博文讲到了其中的一点,就是块大小决定了每个块组最多管理多少个block块。因为块组中用1个block作为位图来之时该块组的某一块是否空闲。
1024----最多有8K个块----------块组大小为8M字节 (1024字节/block*8K块)
2048----最多有16K个块---------块组大小为32M字节
4096----最多有32K个快----------块组大小为128M字节
说block-size重要,不光是因为他决定了块组的一些属性,她还决定了一个ext2文件的属性(最大长度)。我们知道Inode中有个长度为15的数组指向文件的数据存储的块。前12个为直接指针,指向了数据所在的block块。第13 个数组元素是1级间接指针,第14个数组元素为二级间接指针,第15个元素为三级间接指针,通过间接指针,ext2支持的文件最大长度获得了极大的扩展。
文件的组织形式不是这篇博文的重点,我们掠过不细讲
表 1. 各种数据块对应的文件寻址范围
默认情况下为1024。blocksize决定了,总的块数也就决定了(在磁盘空间一定的情况下。比如我们空间就是500MB)。
表 1. 各种数据块对应的文件寻址范围
块大小 | 直接寻址 | 间接寻址 | 二次间接寻址 | 三次间接寻址 |
1024 | 12KB | 268KB | 64.26MB | 16.06GB |
2048 | 24KB | 1.02MB | 513.02MB | 265.5GB |
4096 | 48KB | 4.04MB | 4GB | ~ 4TB |
- linux-tods:/mnt/bean # mke2fs /dev/loop0
- mke2fs 1.41.9 (22-Aug-2009)
- Filesystem label=
- OS type: Linux
- Block size=1024 (log=0)
- Fragment size=1024 (log=0)
- 128016 inodes, 512000 blocks
- 25600 blocks (5.00%) reserved for the super user
- First data block=1
- Maximum filesystem blocks=67633152
- 63 block groups
- 8192 blocks per group, 8192 fragments per group
- 2032 inodes per group
- Superblock backups stored on blocks:
- 8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409
- Writing inode tables: done
- Writing superblocks and filesystem accounting information: done
- This filesystem will be automatically checked every 26 mounts or
- 180 days, whichever comes first. Use tune2fs -c or -i to override.
- linux-tods:/mnt/bean # mke2fs -b 4096 /dev/loop0
- mke2fs 1.41.9 (22-Aug-2009)
- Filesystem label=
- OS type: Linux
- Block size=4096 (log=2)
- Fragment size=4096 (log=2)
- 128000 inodes, 128000 blocks
- 6400 blocks (5.00%) reserved for the super user
- First data block=0
- Maximum filesystem blocks=134217728
- 4 block groups
- 32768 blocks per group, 32768 fragments per group
- 32000 inodes per group
- Superblock backups stored on blocks:
- 32768, 98304
- Writing inode tables: done
- Writing superblocks and filesystem accounting information: done
- This filesystem will be automatically checked every 39 mounts or
- 180 days, whichever comes first. Use tune2fs -c or -i to override.
- linux-tods:/mnt/bean # mke2fs -m 10 /dev/loop0
- mke2fs 1.41.9 (22-Aug-2009)
- Filesystem label=
- OS type: Linux
- Block size=1024 (log=0)
- Fragment size=1024 (log=0)
- 128016 inodes, 512000 blocks
- 51200 blocks (10.00%) reserved for the super user
- First data block=1
- Maximum filesystem blocks=67633152
- 63 block groups
- 8192 blocks per group, 8192 fragments per group
- 2032 inodes per group
- Superblock backups stored on blocks:
- 8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409
- Writing inode tables: done
- Writing superblocks and filesystem accounting information: done
- This filesystem will be automatically checked every 23 mounts or
- 180 days, whichever comes first. Use tune2fs -c or -i to override.
点击(此处)折叠或打开
- linux-tods:/mnt/bean # mke2fs -i 8192 /dev/loop0
- mke2fs 1.41.9 (22-Aug-2009)
- Filesystem label=
- OS type: Linux
- Block size=1024 (log=0)
- Fragment size=1024 (log=0)
- 64008 inodes, 512000 blocks
- 25600 blocks (5.00%) reserved for the super user
- First data block=1
- Maximum filesystem blocks=67633152
- 63 block groups
- ......
- linux-tods:/mnt/bean # dumpe2fs /dev/loop0
- Group 0: (Blocks 1-8192)
- Primary superblock at 1, Group descriptors at 2-3
- Reserved GDT blocks at 4-259
- Block bitmap at 260 (+259), Inode bitmap at 261 (+260)
- Inode table at 262-388 (+261)
- 7790 free blocks, 1005 free inodes, 2 directories
- Free blocks: 403-8192
- Free inodes: 12-1016
- Group 1: (Blocks 8193-16384)
- Backup superblock at 8193, Group descriptors at 8194-8195
- Reserved GDT blocks at 8196-8451
- Block bitmap at 8452 (+259), Inode bitmap at 8453 (+260)
- Inode table at 8454-8580 (+261)
- 7804 free blocks, 1016 free inodes, 0 directories
- Free blocks: 8581-16384
- Free inodes: 1017-2032
- linux-tods:/mnt/bean # mke2fs -i 1524 /dev/loop0
- mke2fs 1.41.9 (22-Aug-2009)
- Filesystem label=
- OS type: Linux
- Block size=1024 (log=0)
- Fragment size=1024 (log=0)
- 344232 inodes, 512000 blocks
- 25600 blocks (5.00%) reserved for the super user
- First data block=1
- Maximum filesystem blocks=67633152
- 63 block groups
- 8192 blocks per group, 8192 fragments per group
- 5464 inodes per group
- Superblock backups stored on blocks:
- Inode count: 128016
- Block count: 512000
- Reserved block count: 25600
- Free blocks: 493526
- Free inodes: 128005
- First block: 1
- Block size: 1024
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