Our validation team noticed that in some configurations mkfs.ext4 with the
-D option creates a filesystem that can't be mounted:
# mkfs.ext4 -D -F /dev/pmem5
mke2fs 1.43.3 (04-Sep-2016)
/dev/pmem5 contains a ext4 file system
last mounted on Tue Jul 26 07:44:19 2016
Creating filesystem with 65027584 4k blocks and 16261120 inodes
Filesystem UUID: 6f95ece9-d4cb-4cfc-bc22-211119d5efe7
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424, 20480000, 23887872
Allocating group tables: done
Writing inode tables: done
Creating journal (262144 blocks): done
Writing superblocks and filesystem accounting information: done
# mount /dev/pmem5 /mnt
mount: wrong fs type, bad option, bad superblock on /dev/pmem5,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so.
where dmesg says:
EXT4-fs (pmem5): ext4_check_descriptors: Block bitmap for group 1 overlaps superblock
EXT4-fs (pmem5): ext4_check_descriptors: Inode bitmap for group 1 overlaps superblock
EXT4-fs (pmem5): ext4_check_descriptors: Inode table for group 1 overlaps superblock
EXT4-fs (pmem5): ext4_check_descriptors: Block bitmap for group 2 overlaps superblock
EXT4-fs (pmem5): ext4_check_descriptors: Inode bitmap for group 2 overlaps superblock
EXT4-fs (pmem5): ext4_check_descriptors: Inode table for group 2 overlaps superblock
...
EXT4-fs (pmem5): ext4_check_descriptors: Block bitmap for group 63 overlaps superblock
EXT4-fs (pmem5): ext4_check_descriptors: Inode bitmap for group 63 overlaps superblock
EXT4-fs (pmem5): ext4_check_descriptors: Inode table for group 63 overlaps superblock
EXT4-fs (pmem5): no journal found
If we omit the "-D" option from mkfs.ext4, everything works. Note also that
this behavior is independent of the DAX mount option.
This isn't blocking us, I just thought you would want to know.
- Ross
