Linux Centos的Inode及Block相關知識

本經驗均在CentOSrelease6.7(Final)下操作，如知識有欠缺之處 歡迎批評指正。
linux 的inode及block的相關知識：
1> Linux系統分區格式化文件系統之後，系統會分為Inode及Block兩部分：
1)Inode為系統文件的屬性信息（ls -l的結果）及指向文件實體的指針，但是沒有存放文件名，一般在上級目錄裡的Block。
2)Block為存放數據的，ext3/ext4一般為1k,2k,4k,一般默認4k
3)一個文件不論多大至少占用一個Inode和一個Block，一個Block只能存放一個文件的內容，block的數量大於Inode的數量，多個文件可以占用同一個 inode(硬鏈接) 。
4）訪問文件, 通過文件-->inode(驗證權限)--->blocks.
5）inode 一般情況默認256B，block大小1k，2k，4k，默認4k,注意，引導分區等特殊分區除外。
6）通過df -i 查看inode的數量及使用情況,dumpe2fs /dev/sda1 查看inode及block的大小和數量。
7）一個block只能 被一個文件使用 ，如果一個文件很小block太大，剩余空間浪費，無法繼續被其他文件使用。
8）block不是越大越好，根據業務的文件大小進行選擇，一般就是默認 4k。
9）可以在格式化的時候改變inode及block的大小，使用mkfs.ext4 -b 2048 -I 1024 /dev/sdb2



2>Linux中df命令的功能是用來檢查linux服務器的文件系統的磁盤空間占用情況。可以利用該命令來獲取硬盤被占用了多少空間，目前還剩下多少空間等信息。
1．命令格式：
df [選項] [文件]
2.參數 :
df -i 查看參數多少 個

[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 查看磁盤大小：

[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

查看當前系統分區的Inode及Block的總量及使用量：

[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分區為128，常規分區為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>添加一塊磁盤，格式化，改變Inode及 Block的大小，掛載查看硬盤的Inode及Block數量：
1）添加一塊5G的磁盤，為方便區分設置為/dev/sdb，fdisk分區，然後mkfs.ext4格式化
（虛擬機增加一塊5G的硬盤，分區，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  ### 為做區分，選擇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.

分區時的參數命令：
   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)    ###默認的Block的大小為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的大小范圍為128-2048,block的大小范圍為1024-4096####
3)將Block和Inode的大小都改為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命令查詢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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