“每个组的Inode”和"lazy_itable_init“标志与ext4文件系统中的"Inode计数”值有什么关系？

Question

我正试图导致一个客户情况，其中两个相同的驱动器，使用相同的命令格式化，导致~55 in的总磁盘空间的差异，因为额外的Inode开销。

我想要理解

1. 关于2 xInodes per group如何转换为2 xInode count的数学
2. 使用Inodes per group标志时如何设置lazy_itable_init

Environment:

这两个驱动器在两个相同的硬件服务器上，运行在相同的操作系统上。以下是这两个驱动器的详细信息(敏感信息已编辑)：

驱车A：

=== START OF INFORMATION SECTION ===
Vendor:               HPE
Product:              <strip>
Revision:             HPD4
Compliance:           SPC-5
User Capacity:        7,681,501,126,656 bytes [7.68 TB]
Logical block size:   512 bytes
Physical block size:  4096 bytes
LU is resource provisioned, LBPRZ=1
Rotation Rate:        Solid State Device
Form Factor:          2.5 inches
Logical Unit id:      <strip>
Serial number:        <strip>
Device type:          disk
Transport protocol:   SAS (SPL-3)
Local Time is:        Mon Apr 25 07:39:27 2022 GMT
SMART support is:     Available - device has SMART capability.

驱动B：

=== START OF INFORMATION SECTION ===
Vendor:               HPE
Product:              <strip>
Revision:             HPD4
Compliance:           SPC-5
User Capacity:        7,681,501,126,656 bytes [7.68 TB]
Logical block size:   512 bytes
Physical block size:  4096 bytes
LU is resource provisioned, LBPRZ=1
Rotation Rate:        Solid State Device
Form Factor:          2.5 inches
Logical Unit id:      <strip>
Serial number:        <strip>
Device type:          disk
Transport protocol:   SAS (SPL-3)
Local Time is:        Mon Apr 25 07:39:23 2022 GMT
SMART support is:     Available - device has SMART capability.

要格式化驱动器的命令是：

sudo mke2fs -F -m 1 -t ext4 -E lazy_itable_init,nodiscard /dev/sdc1

问题：

驱动器A和B的df -h输出分别显示尺寸为6.9T的DriveA和尺寸为7.0T的驱动器B：

/dev/sdc1       6.9T   89M  6.9T   1% /home/<strip>/data/<serial>
...
/dev/sdc1       7.0T  3.0G  6.9T   1% /home/<strip>/data/<serial>

Observations:

• 两个驱动器上的fdisk输出显示它们都有相同的分区。

DriveA：

Disk /dev/sdc: 7681.5 GB, 7681501126656 bytes, 15002931888 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 8192 bytes / 8192 bytes
Disk label type: gpt
Disk identifier: 70627C8E-9F97-468E-8EE6-54E960492318


#         Start          End    Size  Type            Name
 1         2048  15002929151      7T  Microsoft basic primary

DriveB：

Disk /dev/sdc: 7681.5 GB, 7681501126656 bytes, 15002931888 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 8192 bytes / 8192 bytes
Disk label type: gpt
Disk identifier: 702A42FA-9A20-4CE4-B938-83D3AB3DCC49


#         Start          End    Size  Type            Name
 1         2048  15002929151      7T  Microsoft basic primary

• /etc/mke2fs.conf内容在两个系统上都是相同的，因此这里没有有趣的事情：

================== DriveA =================
[defaults]
        base_features = sparse_super,filetype,resize_inode,dir_index,ext_attr
        enable_periodic_fsck = 1
        blocksize = 4096
        inode_size = 256
        inode_ratio = 16384

[fs_types]
        ext3 = {
                features = has_journal
        }
        ext4 = {
                features = has_journal,extent,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize,64bit
                inode_size = 256
        }
...
================== DriveB =================
[defaults]
        base_features = sparse_super,filetype,resize_inode,dir_index,ext_attr
        enable_periodic_fsck = 1
        blocksize = 4096
        inode_size = 256
        inode_ratio = 16384

[fs_types]
        ext3 = {
                features = has_journal
        }
        ext4 = {
                features = has_journal,extent,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize,64bit
                inode_size = 256
        }

• 如果两个驱动器的tune2fs -l输出之间存在差异，则可以看到DriveA上的Inodes per group为2x DriveB。
• 我们还看到Inode count在DriveA上是2xDriveB (完全不同的这里)

DriveA:
    Inode count:              468844544
    Block count:              1875365888
    Reserved block count:     18753658
    Free blocks:              1845578463
    Free inodes:              468843793
    ...
    Fragments per group:      32768
    Inodes per group:         8192
    Inode blocks per group:   512
    Flex block group size:    16
    
DriveB:
    Inode count:              234422272 <----- Half of A
    Block count:              1875365888
    Reserved block count:     18753658
    Free blocks:              1860525018
    Free inodes:              234422261
    ...
    Fragments per group:      32768
    Inodes per group:         4096 <---------- Half of A
    Inode blocks per group:   256  <---------- Half of A
    Flex block group size:    16

• 从如何计算ext2 2文件系统上的“每组Inode块”？我了解到Inode blocks per group是Inodes per group的结果
• 从mke2fs代码(来源)中，只有在提供lazy_itable_init时，才会在write_inode_tables函数中调用Inodes per group值：

write_inode_tables(fs, lazy_itable_init, itable_zeroed);
...
static void write_inode_tables(ext2_filsys fs, int lazy_flag, int itable_zeroed)
...
    if (lazy_flag)
        num = ext2fs_div_ceil((fs->super->s_inodes_per_group - <--------- here
                       ext2fs_bg_itable_unused(fs, i)) *
                      EXT2_INODE_SIZE(fs->super),
                      EXT2_BLOCK_SIZE(fs->super));

如果将inode计数的差值乘以常量inode大小(256)，则得到额外inode开销的(468844544-234422272)*256 = 60012101632 bytes ~55 get。

1. 有人能帮我计算一下，当Inodes per group增加到2倍时，Inode计数是如何增加到2倍的吗？
2. lazy_itable_init在运行时是否会影响到Inodes per group的值，如果是的话，我们如何才能理解它将设置什么值？(此标志是代码中唯一对s_inodes_per_group的引用)

Answer 1

我发现这两种情况的差异是e2fsprogs版本的差异- 1.42.9和1.45.4。我没有想过要检查它，只依赖于mke2fs.conf文件。为这个明显的错过和感谢@lustreone的建议道歉。

我仍然很想知道与每个组的Inode和Inode计数有关的数学。