Centos的Inode及Block相关知识

Centos的Inode及Block相关知识

时间:2016-06-04 01:54 来源:blog.51cto.com  作者:“tao” 博客  举报  点击:173次

本经验均在CentOSrelease6.7(Final)下操作，如知识有欠缺之处 欢迎批评指正。

linux 的inode及block的相关知识：

1>  Linux系统分区格式化文件系统之后，系统会分为Inode及Block两部分：

    1)Inode为系统文件的属性信息（ls -l的结果）及指向文件实体的指针，但是没有存放文件名，一般在上级目录里的Block。

    2)Block为存放数据的，ext3/ext4一般为1k,2k,4k,一般默认4k

    3)一个文件不论多大至少占用一个Inode和一个Block，一个Block只能存放一个文件的内容，block的数量大于Inode的数量，多个文件可以占用同一个 inode(硬链接) 。

    4）访问文件, 通过文件-->inode(验证权限)--->blocks.

    5）inode 一般情况默认256B，block大小1k，2k，4k，默认4k,注意，引导分区等特殊分区除外。

    6）通过df -i 查看inode的数量及使用情况,dumpe2fs /dev/sda1  查看inode及block的大小和数量。

    7）一个block只能 被一个文件使用 ，如果一个文件很小block太大，剩余空间浪费，无法继续被其他文件使用。

    8）block不是越大越好，根据业务的文件大小进行选择，一般就是默认 4k。

    9）可以在格式化的时候改变inode及block的大小，使用mkfs.ext4 -b 2048 -I 1024  /dev/sdb2

 

2>Linux中df命令的功能是用来检查linux服务器的文件系统的磁盘空间占用情况。可以利用该命令来获取硬盘被占用了多少空间，目前还剩下多少空间等信息。
1．命令格式：
df [选项] [文件]

2.参数 :

df -i  查看参数多少 个

[root@techW ~] # df -i
Filesystem            Inodes IUsed   IFree IUse% Mounted on
/dev/mapper/vg_techw-lv_root
                     1152816 55846 1096970    5% /
tmpfs                 125596     1  125595    1%  /dev/shm
/dev/sda1              128016    38  127978    1%  /boot

df -h  查看磁盘大小：

[root@techW ~] # df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_techw-lv_root
                       18G  1.5G   15G   9% /
tmpfs                 491M     0  491M   0%  /dev/shm
/dev/sda1              477M   36M  416M   8%  /boot

 

 

查看当前系统分区的Inode及Block的总量及使用量：

[root@techW ~] # dumpe2fs  /dev/sda1 | grep -i "block size"
dumpe2fs 1.41.12 (17-May-2010)
Block size:               1024
[root@techW ~] #
[root@techW ~] #
[root@techW ~] # dumpe2fs  /dev/sda1 | grep -i "inode size"
dumpe2fs 1.41.12 (17-May-2010)
Inode size:               128     ###boot分区为128，常规分区为256
[root@techW ~] #
[root@techW ~] #
[root@techW ~] # dumpe2fs  /dev/sda1 | grep -i "inode count"
dumpe2fs 1.41.12 (17-May-2010)
Inode count:              128016
[root@techW ~] #
[root@techW ~] # dumpe2fs  /dev/sda1 | grep -i "block count"
dumpe2fs 1.41.12 (17-May-2010)
Block count:              512000
Reserved block count:     25600

3>添加一块磁盘，格式化，改变Inode及 Block的大小，挂载查看硬盘的Inode及Block数量：

1）添加一块5G的磁盘，为方便区分设置为/dev/sdb，fdisk分区，然后mkfs.ext4格式化 

（虚拟机增加一块5G的硬盘，分区，格式化）

[root@techW ~] # fdisk  /dev/sdb
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x2d37eabe.
Changes will remain  in  memory only,  until  you decide to write them.
After that, of course, the previous content won't be recoverable.
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode ( command  'c' ) and change display  units  to
         sectors ( command  'u' ).
Command (m  for  help):  n  ### add a new partition
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 2   ### 为做区分，选择2
First cylinder (1-652, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-652, default 652):
Using default value 652
Command (m  for  help): w    ###  write table to disk and exit
The partition table has been altered!
Calling ioctl() to re- read  partition table.
Syncing disks.

分区时的参数命令：
   a   toggle a bootable flag
   b   edit bsd disklabel
   c   toggle the dos compatibility flag
   d   delete a partition
   l   list known partition types
   m   print this menu
   n   add a new partition
   o   create a new empty DOS partition table
   p   print the partition table
   q   quit without saving changes
   s   create a new empty Sun disklabel
   t   change a partition's system  id
   u   change display /entry  units
   v    verify the partition table
   w   write table to disk and  exit
   x   extra functionality (experts only)

 

[root@techW ~] # mkfs.ext4 /dev/sdb2
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS  type : Linux
Block size=4096 (log=2)     ###默认的Block的大小为4096
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
327680 inodes, 1309289 blocks
65464 blocks (5.00%) reserved  for  the super user
First data block=0
Maximum filesystem blocks=1342177280
40 block  groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736
Writing inode tables:  done
Creating journal (32768 blocks):  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.

 

2）###inode的大小范围为128-2048,block的大小范围为1024-4096####

 

3)将Block和Inode的大小都改为2048：

[root@techW ~] # mkfs.ext4 -b 2048 -I 2048 /dev/sdb2
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
326400 inodes, 2618578 blocks
130928 blocks (5.00%) reserved  for  the super user
First data block=0
Maximum filesystem blocks=540016640
160 block  groups
16384 blocks per group, 16384 fragments per group
2040 inodes per group
Superblock backups stored on blocks:
        16384, 49152, 81920, 114688, 147456, 409600, 442368, 802816, 1327104,
        2048000
Writing inode tables:  done
Creating journal (32768 blocks):  done
Writing superblocks and filesystem accounting information:  done
This filesystem will be automatically checked every 30 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

 

4)使用dumpe2fs命令查询Inode和Block的大小：

[root@techW ~] # dumpe2fs  /dev/sdb2 | grep "Inode size"
dumpe2fs 1.41.12 (17-May-2010)
Inode size:               2048   ###大小更改成功
[root@techW ~] #
s   /dev/sdb2  |  grep  "Block size"
dumpe2fs 1.41.12 (17-May-2010)
Block size:               2048   ###大小更改成功