在Linux中进行格式化必须考虑Block与inode，Block还好理解，它是磁盘可以记录的最小单位，是由数个扇区组成，所以大小通常为n*512Bytes，例如4K。 那么inode是什么呢 ？ Block是记录文件内容的区域，inode则是记录该文件的属性及其放置在哪个Block之内的信息。每个inode分别记录一个档案的属性与这个档案分布在哪些datablock上(也就是我们说的指针,有的地方也叫索引编号)。

具体如下：

● inode 编号　　  ● 用来识别文件类型，以及用于 stat C 函数的模式信息 　 ● 文件的链接数目　 ● 属主的 UID　● 最近一次访问的时间   ● 属主的组 ID(GID)　 ● 文件的大小　　● 文件所使用的磁盘块的实际数目　　● 最近一次修改的时间　　　　● 最近一次更改的时间

小结：inode两个功能：记录档案属性和指针所以，每个文件都会占用一个inode。当Linux系统要查找某个文件时，它会先搜索inode table找到这个文件的属性及数据存放地点，然后再查找数据存放的Block进而将数据取出。一个分区被格式化为一个文件系统之后，基本上它一定会有inode table与数据区域两大块，一个用来记录文件的属性信息与该文件存放的Block块，一个用来记录文件的内容。

一个逻辑上的概念： 一个block对应一个inode吗？   答案是否定的，一个大文件虽然占用很多的block，但是只使用了一个inode

测试1： 我添加磁盘并划分分区,/dev/sdb5,6,7各100M 并指定block大小分别是1k,2k,4k格式化时得到结构inode数量都是28000多 (-b)

结论：inode和block没有直接关系！网上有一种说说“block越大，inode越小的说法”显然错误

测试2： 我使用-i 选项格式化 (-i bytes-per-inode

Specify the bytes/inode ratio.   mke2fs  creates  an  inode  for every  bytes-per-inode  bytes  of space on the disk.  The larger the bytes-per-inode ratio, the fewer  inodes  will  be  created. This  value generally shouldn’t be smaller than the blocksize of the filesystem, since in that case more  inodes  would  be  made than  can  ever  be  used.  Be warned that it is not possible to expand the number of inodes on a filesystem after it is created, so be careful deciding the correct value for this parameter.

)

结论：指定i越小，inode越大，注意这还是和block没关系！只是用户自定义inode数量而已！

注意：一个文件占用一个inode，但是至少占用一个block,不管block数量有多大，1K，2K，4K，文件小于blocksize时，占用一个block，此block的剩余空间别的文件无法使用！若文件大于blocksize时，直接使用多个block

于是，就有了最终结论：(当然这里不是细算！)

分区总量/block大小 >= inode数  ------  > 能创建的文件数量的最大值 = inode数

分区总量/block大小  < inode数  --------> 能创建的文件数量的最大值 = 分区总量/block大小的数量个文件

若分区是提供给给大文件应用，一般不做考虑

相反，若分区是提供给小文件应用，则一定要自己计算并格式化，以免inode耗尽，磁盘分区却未使用完

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测试1数据：

[root@desktop132 ~]# mkfs.ext3 -b 1024 /dev/sdb5

mke2fs 1.41.12 (17-May-2010)

Filesystem label=

OS type: Linux

Block size=1024 (log=0)

Fragment size=1024 (log=0)

Stride=0 blocks, Stripe width=0 blocks

28112 inodes, 112392 blocks

5619 blocks (5.00%) reserved for the super user

First data block=1

Maximum filesystem blocks=67371008

14 block groups

8192 blocks per group, 8192 fragments per group

2008 inodes per group

Superblock backups stored on blocks:

8193, 24577, 40961, 57345, 73729

Writing inode tables: done

Creating journal (4096 blocks): done

Writing superblocks and filesystem accounting information: done

[root@desktop132 ~]# mkfs.ext3 -b 2048 /dev/sdb6

mke2fs 1.41.12 (17-May-2010)

Filesystem label=

OS type: Linux

Block size=2048 (log=1)

Fragment size=2048 (log=1)

Stride=0 blocks, Stripe width=0 blocks

28160 inodes, 56210 blocks

2810 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=57671680

4 block groups

16384 blocks per group, 16384 fragments per group

7040 inodes per group

Superblock backups stored on blocks:

16384, 49152

Writing inode tables: done

Creating journal (4096 blocks): done

Writing superblocks and filesystem accounting information: done

[root@desktop132 ~]# mkfs.ext3 -b 4096 /dev/sdb7

mke2fs 1.41.12 (17-May-2010)

Filesystem label=

OS type: Linux

Block size=4096 (log=2)

Fragment size=4096 (log=2)

Stride=0 blocks, Stripe width=0 blocks

28128 inodes, 28105 blocks

1405 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=29360128

1 block group

32768 blocks per group, 32768 fragments per group

28128 inodes per group

Writing inode tables: done

Creating journal (1024 blocks): done

Writing superblocks and filesystem accounting information: done

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测试2数据：

[root@desktop132 ~]# mkfs.ext3 -i 1024 /dev/sdb5

mke2fs 1.41.12 (17-May-2010)

Filesystem label=

OS type: Linux

Block size=1024 (log=0)

Fragment size=1024 (log=0)

Stride=0 blocks, Stripe width=0 blocks

112448 inodes, 112392 blocks

5619 blocks (5.00%) reserved for the super user

First data block=1

Maximum filesystem blocks=67371008

14 block groups

8192 blocks per group, 8192 fragments per group

8032 inodes per group

Superblock backups stored on blocks:

8193, 24577, 40961, 57345, 73729

Writing inode tables: done

Creating journal (4096 blocks): done

Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 31 mounts or

180 days, whichever comes first.  Use tune2fs -c or -i to override.

[root@desktop132 ~]# mkfs.ext3 -i 2048 /dev/sdb6

mke2fs 1.41.12 (17-May-2010)

Filesystem label=

OS type: Linux

Block size=1024 (log=0)

Fragment size=1024 (log=0)

Stride=0 blocks, Stripe width=0 blocks

56224 inodes, 112420 blocks

5621 blocks (5.00%) reserved for the super user

First data block=1

Maximum filesystem blocks=67371008

14 block groups

8192 blocks per group, 8192 fragments per group

4016 inodes per group

Superblock backups stored on blocks:

8193, 24577, 40961, 57345, 73729

Writing inode tables: done

Creating journal (4096 blocks): done

Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 35 mounts or

180 days, whichever comes first.  Use tune2fs -c or -i to override.

[root@desktop132 ~]# mkfs.ext3 -i 4096 /dev/sdb7

mke2fs 1.41.12 (17-May-2010)

Filesystem label=

OS type: Linux

Block size=1024 (log=0)

Fragment size=1024 (log=0)

Stride=0 blocks, Stripe width=0 blocks

28112 inodes, 112420 blocks

5621 blocks (5.00%) reserved for the super user

First data block=1

Maximum filesystem blocks=67371008

14 block groups

8192 blocks per group, 8192 fragments per group

2008 inodes per group

Superblock backups stored on blocks:

8193, 24577, 40961, 57345, 73729

Writing inode tables: done

Creating journal (4096 blocks): done

Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 37 mounts or

180 days, whichever comes first.  Use tune2fs -c or -i to override.

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