8
26
2014
1

ext4文件系统浅析----跨度之大的inode号

最近在研究ext4文件系统,系统同道之人能共同研究、探讨

 

背景:

在根目录底下

root@f303server:/mnt/sde3# ls -i

     14 2.txt   786433 dir1  1048577 dir3        1179649 mkfs

     15 3.txt   917505 dir2       11 lost+found       13 sde3.txt

 

问题:

用黄色标记的几个为目录项,其中lost+found是格式化、挂载文件系统时自带的目录,其余四个是我创建的。那么问题来了,为什么我创建目录结点的inode号那么的大?

 

 

解释:

在ext4中,文件系统为了保证数据能更加均匀地分布在磁盘上,所以在创建目录时,尽量均匀地分布在不同的flexible block_group(flexbg)中。且同一个目录下的文件和这个目录的inode号在一个flexbg中:

 

默认一个flexbg含有16个block group,故 一个flexbg中含有inode结点数为8196 * 16 = 131072 个。所以dir1786433 位于第6flexbg中(131072 * 6 + 1 = 786433,在dir1目录下的1.txt,查看其inode结点号为  786434

 

同理可以计算其他的三个目录分别在第789flexbg

 

 

 

ps:

1怎么查看一个group有多少个inode结点:

debugfs /dev/sde3

stats

显示如下

 

debugfs

Stats
Filesystem volume name:   <none>
Last mounted on:          /mnt/sde3
Filesystem UUID:          fea02b9a-41d1-4bf1-96ce-d3298d67778f
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery extent 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:              1310720
Block count:              5242880
Reserved block count:     262144
Free blocks:              5116587
Free inodes:              1310705
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      1022
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         8192
Inode blocks per group:   512  #Inode table所占的块数目
Flex block group size:    16         #下面前16个inode bitmap所在
Filesystem created:       Mon Jul 28 08:40:58 2014
Last mount time:          Tue Jul 29 19:53:03 2014
Last write time:          Tue Jul 29 19:53:03 2014
Mount count:              8
Maximum mount count:      -1
Last checked:             Mon Jul 28 08:40:58 2014
Check interval:           0 (<none>)
Lifetime writes:          454 MB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:               256
Required extra isize:     28
Desired extra isize:      28
Journal inode:            8
Default directory hash:   half_md4
Directory Hash Seed:      0da457a4-59ff-402a-9181-c66156ea5991
Journal backup:           inode blocks
Directories:              6
Group  0: block bitmap at 1025, inode bitmap at 1041, inode table at 1057
           23513 free blocks, 8178 free inodes, 2 used directories, 8176 unused inodes
           [Checksum 0x7a6d]
 Group  1: block bitmap at 1026, inode bitmap at 1042, inode table at 1569
           31740 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
           [Inode not init, Checksum 0x2c05]
 Group  2: block bitmap at 1027, inode bitmap at 1043, inode table at 2081
           32768 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
           [Inode not init, Block not init, Checksum 0x7c29]
 Group  3: block bitmap at 1028, inode bitmap at 1044, inode table at 2593
           31743 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
           [Inode not init, Checksum 0x1e2b]延迟初始化
………..
……..
Group 12: block bitmap at 1037, inode bitmap at 1053, inode table at 7201
           32768 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
           [Inode not init, Block not init, Checksum 0x30ab]
 Group 13: block bitmap at 1038, inode bitmap at 1054, inode table at 7713
           32768 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
           [Inode not init, Block not init, Checksum 0x8f81]
 Group 14: block bitmap at 1039, inode bitmap at 1055, inode table at 8225
           32768 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
           [Inode not init, Block not init, Checksum 0x8aa2]
 Group 15: block bitmap at 1040, inode bitmap at 1056, inode table at 8737
           32768 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
           [Inode not init, Block not init, Checksum 0x350d]
 Group 16: block bitmap at 524288, inode bitmap at 524304, inode table at 524320
           24544 free blocks, 8192 free inodes, 0 used directories, 8192 unused inodes
           [Inode not init, Checksum 0xb89c]

 

 

2.怎么查看flexbg包含16个block group

从上面的debugfs的group 显示结果可以看出,group 0至group 15的block bitmap,inode bitmap、inode table是连续存放的。而从group 16开始元数据不再连续了,这也说明flexbg为16个block group。

Category: 文件系统 | Tags: ext4 | Read Count: 2972
Avatar_small
AP 10th Social Quest 说:
2022年9月10日 19:35

Social Study is most important students to all students of AP 10th Class, here we have provided the study material with solved question bank for all government and private school TM, EM, UM and HM students in chapter wise from past years old exams and we have provided the AP 10th Social Model Paper 2023 Pdf suggested by subject experts. AP 10th Social Question Paper All BSEAP 10th class regular and private course students can follow the list of chapters under SSC Social Study to practice study material with previous question bank to get a better score in summative assessment (SA) and formative assessment (FA) SA-1, SA-2, FA-1, FA-2, FA-3, FA-4 along with Assignments exams previously called Unit Test-1, Unit Test-2, Unit Test-3, Unit Test-4 and Three Months.


登录 *


loading captcha image...
(输入验证码)
or Ctrl+Enter

Host by is-Programmer.com | Power by Chito 1.3.3 beta | Theme: Aeros 2.0 by TheBuckmaker.com