Linux磁盘预留空间

刚才发现df -B GiB返回的结果中，总大小!=已用+可用

$ df -B GiB
文件系统           1GiB的块    已用           可用   已用% 挂载点
/dev/sdb1         1834GiB    1740GiB       1GiB   100% /mnt/test

后来才发现系统会预留空间

通过命令tune2fs -l查看

$ sudo tune2fs -l /dev/sdb1 
tune2fs 1.47.0 (5-Feb-2023)
Filesystem volume name:   <none>
Last mounted on:          /mnt/MyPassport
Filesystem UUID:          fksosu28-koe7-2144-sk70-07isos02j83d
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery extent 64bit flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize
Filesystem flags:         signed_directory_hash 
Default mount options:    user_xattr acl
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              122093568
Block count:              488369920
Reserved block count:     24418496
Overhead clusters:        7717326
Free blocks:              30932023
Free inodes:              122090191
First block:              0
Block size:               4096
Fragment size:            4096
Group descriptor size:    64
Reserved GDT blocks:      1024
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         8192
Inode blocks per group:   512
Flex block group size:    16
Filesystem created:       Mon Feb 13 15:40:26 2023
Last mount time:          Mon May 20 18:29:54 2024
Last write time:          Mon May 27 08:37:41 2024
Mount count:              553
Maximum mount count:      -1
Last checked:             Thu Jan  1 08:00:00 1970
Check interval:           0 (<none>)
Lifetime writes:          113 TB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:              256
Required extra isize:     32
Desired extra isize:      32
Journal inode:            8
Default directory hash:   half_md4
Directory Hash Seed:      78afbd79-ddfc-f7a9-ec61-fb33aff8ea31
Journal backup:           inode blocks

其中

Reserved block count: 24418496就是预留的块的数量

Block size: 4096就是每一个块的大小

预留空间:$$\displaystyle\frac{(24418496\times4096)}{2^{30}}\approx93.15GiB$$

预留比例:$$\displaystyle\frac{24418496}{488369920}\times100\%=5\%$$

这也就解释了为什么总大小!=已用+可用

$ df -B GiB
文件系统           1GiB的块    已用           可用   已用% 挂载点
/dev/sdb1         1834GiB    1740GiB       1GiB   100% /mnt/test

已用+可用+预留≈总空间

$$\displaystyle1740+1+93.15=1834.15\approx1834$$

其他零零碎碎的小块懒得管了