修复super block

修复super block

root@test-server:~# dumpe2fs /dev/sde1
dumpe2fs 1.39 (29-May-2006)
dumpe2fs: Bad magic number in super-block while trying to open /dev/sde1
Couldn't find valid filesystem superblock.
root@test-server:~# mke2fs -n /dev/sde1
mke2fs 1.39 (29-May-2006)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
1251712 inodes, 2500107 blocks
125005 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2562719744
77 block groups
32768 blocks per group, 32768 fragments per group
16256 inodes per group
Superblock backups stored on blocks: 
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632


root@test-server:~# mke2fs -b 32768 /dev/sde1
Warning: blocksize 32768 not usable on most systems.
mke2fs 1.39 (29-May-2006)
mke2fs: 32768-byte blocks too big for system (max 4096)
Proceed anyway? (y,n) y
Warning: 32768-byte blocks too big for system (max 4096), forced to continue
Filesystem label=
OS type: Linux
Block size=32768 (log=5)
Fragment size=32768 (log=5)
313600 inodes, 312513 blocks
15625 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=335503360
5 block groups
65528 blocks per group, 65528 fragments per group
62720 inodes per group
Superblock backups stored on blocks: 
65528, 196584
root@test-server:/# dumpe2fs /dev/sde1
dumpe2fs 1.39 (29-May-2006)
Filesystem volume name:   <none>
Last mounted on:          <not available>
Filesystem UUID:          5a41f602-e9f9-4e93-a7f0-c43c2fe12223
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      resize_inode dir_index filetype sparse_super large_file
Default mount options:    (none)
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              313600
Block count:              312513
Reserved block count:     15625
Free blocks:              311257
Free inodes:              313589
First block:              0
Block size:               32768
Fragment size:            32768
Reserved GDT blocks:      4
Blocks per group:         65528
Fragments per group:      65528
Inodes per group:         62720
Inode blocks per group:   245
Filesystem created:       Sat Dec 12 11:46:19 2015
Last mount time:          n/a
Last write time:          Sat Dec 12 11:46:19 2015
Mount count:              0
Maximum mount count:      34
Last checked:             Sat Dec 12 11:46:19 2015
Check interval:           15552000 (6 months)
Next check after:         Thu Jun  9 11:46:19 2016
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:  128
Default directory hash:   tea
Directory Hash Seed:      ac3e3fad-b1e3-4af1-9da0-30d968cbfd44




Group 0: (Blocks 0-65527)
  Primary superblock at 0, Group descriptors at 1-1
  Reserved GDT blocks at 2-5
  Block bitmap at 6 (+6), Inode bitmap at 7 (+7)
  Inode table at 8-252 (+8)
  65272 free blocks, 62709 free inodes, 2 directories
  Free blocks: 256-65527
  Free inodes: 12-62720
Group 1: (Blocks 65528-131055)
  Backup superblock at 65528, Group descriptors at 65529-65529
  Reserved GDT blocks at 65530-65533
  Block bitmap at 65534 (+6), Inode bitmap at 65535 (+7)
  Inode table at 65536-65780 (+8)
  65275 free blocks, 62720 free inodes, 0 directories
  Free blocks: 65781-131055
  Free inodes: 62721-125440
Group 2: (Blocks 131056-196583)
  Block bitmap at 131056 (+0), Inode bitmap at 131057 (+1)
  Inode table at 131058-131302 (+2)
  65281 free blocks, 62720 free inodes, 0 directories
  Free blocks: 131303-196583
  Free inodes: 125441-188160
Group 3: (Blocks 196584-262111)
  Backup superblock at 196584, Group descriptors at 196585-196585
  Reserved GDT blocks at 196586-196589
  Block bitmap at 196590 (+6), Inode bitmap at 196591 (+7)
  Inode table at 196592-196836 (+8)
  65275 free blocks, 62720 free inodes, 0 directories
  Free blocks: 196837-262111
  Free inodes: 188161-250880
Group 4: (Blocks 262112-312512)
  Block bitmap at 262112 (+0), Inode bitmap at 262113 (+1)
  Inode table at 262114-262358 (+2)
  50154 free blocks, 62720 free inodes, 0 directories
  Free blocks: 262359-312512
  Free inodes: 250881-313600


Writing inode tables: done                            
Writing superblocks and filesystem accounting information: done


This filesystem will be automatically checked every 34 mounts or

180 days, whichever comes first.  Use tune2fs -c or -i to override.

Inode和Block相关知识

硬盘格式化的时候，操作系统自动将硬盘分成两个区域。一个是数据区，存放文件数据；另一个是inode区（inode table），存放inode所包含的信息。每个inode节点的大小，一般是128字节或256字节。inode节点的总数，在格式化时就给定，一般是每1KB或每2KB就设置一个inode。假定在一块1GB的硬盘中，每个inode节点的大小为128字节，每1KB就设置一个inode，那么inode table的大小就会达到128MB，占整块硬盘的12.8%。

每个inode都有一个号码，操作系统用inode号码来识别不同的文件。Unix/Linux系统内部不使用文件名，而使用inode号码来识别文件。对于系统来说，文件名只是inode号码便于识别的别称或者绰号。表面上，用户通过文件名，打开文件。实际上，系统内部这个过程分成三步：首先，系统找到这个文件名对应的inode号码；其次，通过inode号码，获取inode信息；最后，根据inode信息，找到文件数据所在的block，读出数据。文件储存在硬盘上，硬盘的最小存储单位叫做"扇区"（Sector）。每个扇区储存512字节（相当于0.5KB）。操作系统读取硬盘的时候，不会一个个扇区地读取，这样效率太低，而是一次性连续读取多个扇区，即一次性读取一个"块"（block）。这种由多个扇区组成的"块"，是文件存取的最小单位。"块"的大小，最常见的是4KB，即连续八个 sector组成一个 block。文件数据都储存在"块"中，必须找到一个地方储存文件的元信息，比如文件的创建者、文件的创建日期、文件的大小等等。这种储存文件元信息的区域就叫做inode，中文译名为"索引节点"。