s tune2fs -l /dev/md0 
Password:
tune2fs 1.42.4 (12-June-2012)
Filesystem volume name:   rootfs-raid
Last mounted on:          /
Filesystem UUID:          b4fcc4bf-620c-4d05-86c5-c871a825fb4c
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:              4644864
Block count:              18554801
Reserved block count:     927740
Free blocks:              1227172
Free inodes:              3456544
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      1019
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 Mar 19 14:00:55 2012
Last mount time:          Thu Jun 21 10:05:00 2012
Last write time:          Thu Jun 21 08:34:58 2012
Mount count:              1
Maximum mount count:      6
Last checked:             Thu Jun 21 08:34:58 2012
Check interval:           604800 (1 week)
Next check after:         Thu Jun 28 08:34:58 2012
Lifetime writes:          349 GB
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
First orphan inode:       1209307
Default directory hash:   half_md4
Directory Hash Seed:      9ecd7b8b-dc69-407d-836d-cf3340133203
Journal backup:           inode blocks