释放硬盘的隐藏空间

时间：2007-01-03 来源：nait

ext3文件系统会root用户按一定比例保留一部分空间以便在分区填满后root用户人能正常操作磁盘。用tune2fs工具可以查看文件系统的一些参数，例如：

root@leo: pts/2: 50 files 18Mb -> tune2fs -l /dev/hdb7
tune2fs 1.37 (21-Mar-2005)
Filesystem volume name:   <none>
Last mounted on:          <not available>
Filesystem UUID:          b6ed8742-b82a-4ab5-969f-d87bb6cd94a3
Filesystem magic number: 0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal filetype sparse_super
Default mount options:    (none)
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              10993664
Block count:              21968879
Reserved block count:     1098443
Free blocks:              21615680
Free inodes:              10993653
First block:              0
Block size:               4096
Fragment size:            4096
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         16384
Inode blocks per group:   512
Filesystem created:       Fri Dec 29 18:51:30 2006
Last mount time:          Fri Dec 29 22:41:55 2006
Last write time:          Fri Dec 29 23:42:16 2006
Mount count:              1
Maximum mount count:      27
Last checked:             Fri Dec 29 18:51:30 2006
Check interval:           15552000 (6 months)
Next check after:         Wed Jun 27 18:51:30 2007
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:               128
Journal inode:            8
Default directory hash:   tea
Directory Hash Seed:      e8c198d0-4f67-413b-a57b-422688838aff
Journal backup:           inode blocks

其中Reserved block count一行就是为root用户所保留的块数，而每块大小是4096,也就是4k，这样当分区大小为90G时，就会有4G多的空间会被作为保留空间而使得普通用户不能使用，如果这个分区只是用来装载数据的普通分区，就没有必要这么浪费了，还是自己动手来释放一些空间吧。

还是用tune2fs工具。过程如下：

root@leo: pts/2: 50 files 18Mb -> df /mnt/backup/ -h
Filesystem            Size Used Avail Use% Mounted on
/dev/hdb7              83G   33M   79G   1% /mnt/backup

root@leo: pts/2: 50 files 18Mb -> umount /mnt/backup/

root@leo: pts/2: 50 files 18Mb -> tune2fs -r 1000 /dev/hdb7
tune2fs 1.37 (21-Mar-2005)
Setting reserved blocks count to 1000

root@leo: pts/2: 50 files 18Mb -> mount /mnt/backup/

root@leo: pts/2: 50 files 18Mb -> df /mnt/backup/ -h
Filesystem            Size Used Avail Use% Mounted on
/dev/hdb7              83G   33M   83G   1% /mnt/backup

root@leo: pts/2: 50 files 18Mb -> tune2fs -l /dev/hdb7
tune2fs 1.37 (21-Mar-2005)
Filesystem volume name:   <none>
Last mounted on:          <not available>
Filesystem UUID:          b6ed8742-b82a-4ab5-969f-d87bb6cd94a3
Filesystem magic number: 0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal filetype needs_recovery sparse_super
Default mount options:    (none)
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              10993664
Block count:              21968879
Reserved block count:     1000
Free blocks:              21615680
Free inodes:              10993653
First block:              0
Block size:               4096
Fragment size:            4096
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         16384
Inode blocks per group:   512
Filesystem created:       Fri Dec 29 18:51:30 2006
Last mount time:          Tue Jan 2 10:00:33 2007
Last write time:          Tue Jan 2 10:00:33 2007
Mount count:              3
Maximum mount count:      27
Last checked:             Fri Dec 29 18:51:30 2006
Check interval:           15552000 (6 months)
Next check after:         Wed Jun 27 18:51:30 2007
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:               128
Journal inode:            8
Default directory hash:   tea
Directory Hash Seed:      e8c198d0-4f67-413b-a57b-422688838aff
Journal backup:           inode blocks

可以看到，当Reserved block count被设置为1000后，用df查看空间，原来的Avail一列由79G变成了84G，增加了4G！