Centos的Inode和Block的相关知识

2020-06-21 12:51:03

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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

Centos,Inode,Block

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 -iFilesystem            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 -hFilesystem            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:              512000Reserved 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/sdbDevice contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabelBuilding 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 partitionCommand action   e   extended   p   primary partition (1-4)pPartition number (1-4): 2  ### 为做区分，选择2First cylinder (1-652, default 1): Using default value 1Last cylinder, +cylinders or +size{K,M,G} (1-652, default 652): Using default value 652Command (m for help): w   ###  write table to disk and exitThe 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 flagb   edit bsd disklabelc   toggle the dos compatibility flagd   delete a partitionl   list known partition typesm   print this menun   add a new partitiono   create a new empty DOS partition tablep   print the partition tableq   quit without saving changess   create a new empty Sun disklabelt   change a partition's system idu   change display/entry unitsv   verify the partition tablew   write table to disk and exitx   extra functionality (experts only)

[root@techW ~]# mkfs.ext4 /dev/sdb2mke2fs 1.41.12 (17-May-2010)Filesystem label=OS type: LinuxBlock size=4096 (log=2)    ###默认的Block的大小为4096Fragment size=4096 (log=2)Stride=0 blocks, Stripe width=0 blocks327680 inodes, 1309289 blocks65464 blocks (5.00%) reserved for the super userFirst data block=0Maximum filesystem blocks=134217728040 block groups32768 blocks per group, 32768 fragments per group8192 inodes per groupSuperblock backups stored on blocks:         32768, 98304, 163840, 229376, 294912, 819200, 884736Writing inode tables: done                            Creating journal (32768 blocks): doneWriting superblocks and filesystem accounting information: doneThis filesystem will be automatically checked every 26 mounts or180 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/sdb2mke2fs 1.41.12 (17-May-2010)Filesystem label=OS type: LinuxBlock size=2048 (log=1)Fragment size=2048 (log=1)Stride=0 blocks, Stripe width=0 blocks326400 inodes, 2618578 blocks130928 blocks (5.00%) reserved for the super userFirst data block=0Maximum filesystem blocks=540016640160 block groups16384 blocks per group, 16384 fragments per group2040 inodes per groupSuperblock backups stored on blocks:         16384, 49152, 81920, 114688, 147456, 409600, 442368, 802816, 1327104,         2048000Writing inode tables: done                            Creating journal (32768 blocks): doneWriting superblocks and filesystem accounting information: doneThis filesystem will be automatically checked every 30 mounts or180 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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