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Centos的Inode和Block的相关知识

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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

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