Centos的Inode和Block的相关知识

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
FilesystemInodes IUsed IFree IUse% Mounted on
/dev/mapper/vg_techw-lv_root
 1152816 55846 10969705% /
tmpfs 125596 11255951% /dev/shm
/dev/sda1 128016381279781% /boot

df -h 查看磁盘大小：

[root@techW ~]# df -h
FilesystemSizeUsed Avail Use% Mounted on
/dev/mapper/vg_techw-lv_root
 18G1.5G 15G 9% /
tmpfs 491M 0491M 0% /dev/shm
/dev/sda1 477M 36M416M 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