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
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