如果在大小小于 512 MB 的逻辑卷中创建文件，则文件的出生时间会丢失

Question

我的系统中有一个卷组，是用单个物理卷创建的。

我正在创建两个逻辑卷 - 一个大小为 100M，另一个大小为 512M。

在LV上创建的100M大小的文件不显示出生时间属性。512M尺寸的LV没有这个问题。

有什么线索可以解释为什么会这样吗？

物理卷和卷组：

# pvdisplay
  --- Physical volume ---
  PV Name               /dev/sda4
  VG Name               VG_System
  PV Size               400.00 GiB / not usable 4.00 MiB
  Allocatable           yes
  PE Size               4.00 MiB
  Total PE              102399
  Free PE               38099
  Allocated PE          64300
  PV UUID               Awnq0n-24v1-Z53P-MC09-3Fvv-dc0r-6QvAyX


# vgdisplay VG_System
  --- Volume group ---
  VG Name               VG_System
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  25
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                24
  Open LV               22
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               <400.00 GiB
  PE Size               4.00 MiB
  Total PE              102399
  Alloc PE / Size       64300 / 251.17 GiB
  Free  PE / Size       38099 / 148.82 GiB
  VG UUID               Zg53rH-kuCI-dWKa-Uo3H-Mr2i-G2As-Wflm0d

第一个LV：

# lvcreate --stripes 1 -n testing -L 100M VG_System
  Logical volume "testing" created.

# mkfs.ext4 /dev/VG_System/testing
mke2fs 1.45.6 (20-Mar-2020)
Discarding device blocks: done
Creating filesystem with 102400 1k blocks and 25688 inodes
Filesystem UUID: ac9c1782-7770-4031-bad8-9b76f7577467
Superblock backups stored on blocks:
        8193, 24577, 40961, 57345, 73729

Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done


# blkid /dev/VG_System/testing
/dev/VG_System/testing: UUID="ac9c1782-7770-4031-bad8-9b76f7577467" BLOCK_SIZE="1024" TYPE="ext4"

# mount /dev/VG_System/testing /mnt/test
# mount | grep test
/dev/mapper/VG_System-testing on /mnt/test type ext4 (rw,relatime,stripe=4)

# touch /mnt/test/a
# stat /mnt/test/a
  File: /mnt/test/a
  Size: 0               Blocks: 0          IO Block: 1024   regular empty file
Device: 252,23  Inode: 12          Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2023-04-13 22:13:43.000000000 +0530
Modify: 2023-04-13 22:13:43.000000000 +0530
Change: 2023-04-13 22:13:43.000000000 +0530
 Birth: -

这里该Birth字段是空的。

第二个LV：

# lvcreate  -n testing2 -L 512M VG_System
  Logical volume "testing2" created.

# mkfs.ext4 /dev/VG_System/testing2
mke2fs 1.45.6 (20-Mar-2020)
Discarding device blocks: done
Creating filesystem with 131072 4k blocks and 32768 inodes
Filesystem UUID: 0b5e24a9-cdf1-4749-9089-bf0cf1495185
Superblock backups stored on blocks:
        32768, 98304

Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done


# blkid /dev/VG_System/testing2
/dev/VG_System/testing2: UUID="0b5e24a9-cdf1-4749-9089-bf0cf1495185" BLOCK_SIZE="4096" TYPE="ext4"

# mount /dev/VG_System/testing2 /mnt/test2
# mount | grep test
/dev/mapper/VG_System-testing2 on /mnt/test2 type ext4 (rw,relatime)

# touch /mnt/test2/a
# stat /mnt/test2/a
  File: /mnt/test2/a
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 252,24  Inode: 12          Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2023-04-13 22:19:01.873047858 +0530
Modify: 2023-04-13 22:19:01.873047858 +0530
Change: 2023-04-13 22:19:01.873047858 +0530
 Birth: 2023-04-13 22:19:01.873047858 +0530

请注意确定它是否相关，但第一个 LV 的安装选项有stripe=4，而第二个 LV 没有此选项。除此之外，两个 LV 都是相似的。

# lvdisplay VG_System/testing
  --- Logical volume ---
  LV Path                /dev/VG_System/testing
  LV Name                testing
  VG Name                VG_System
  LV UUID                n19sRr-SqHW-znjI-0fEW-MkQX-JRUn-MTmZHF
  LV Write Access        read/write
  LV Creation host, time controller, 2023-04-13 22:12:45 +0530
  LV Status              available
  # open                 0
  LV Size                100.00 MiB
  Current LE             25
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:23


# lvdisplay VG_System/testing2
  --- Logical volume ---
  LV Path                /dev/VG_System/testing2
  LV Name                testing2
  VG Name                VG_System
  LV UUID                94oJKP-r2Ob-ReHr-sDSO-t3HY-isJB-ZtEPsq
  LV Write Access        read/write
  LV Creation host, time controller, 2023-04-13 22:18:01 +0530
  LV Status              available
  # open                 1
  LV Size                512.00 MiB
  Current LE             128
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:24

Answer 1

这不是 LVM 的问题。这是 Ext4 的问题。

当文件系统大小小于 512 MB 时，Ext4 使用 Default Inode Size = 128 Bytes ，这不足以存储“扩展元数据”。

当文件系统大小超过 512 MB 时，Ext4 使用默认 Inode Size = 256 Bytes ，这足以存储“扩展元数据”，包括“出生时间”@偏移量 0x90 和偏移量 0x94。

更多详细信息：
https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout#Inode_Table

你可以试试这个：

mkfs.ext4 -I 256 /dev/VG_System/testing  

这将强制较小文件系统上的 Inode Size = 256。

更多详细信息：
https://manpages.debian.org/bullseye/e2fsprogs/mke2fs.8.en.html