user@box:~$ sudo tune2fs -l /dev/md99
[sudo] password for user:
tune2fs 1.42.9 (4-Feb-2014)
Filesystem volume name: <nuser>
Last mounted on: /mnt/md50
Filesystem UUID: 976a8655-2619-4587-878c-dab07f7b7652
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: 244187136
Block count: 1953473536
Reserved block count: 97673676
Free blocks: 665750586
Free inodes: 213815139
First block: 0
Block size: 4096
Fragment size: 4096
Reserved GDT blocks: 558
Blocks per group: 32768
Fragments per group: 32768
Inodes per group: 4096
Inode blocks per group: 256
RAID stride: 128
RAID stripe width: 1048320
Flex block group size: 16
Filesystem created: Wed Dec 28 16:17:14 2016
Last mount time: Fri Jun 23 12:48:18 2017
Last write time: Fri Jun 23 12:48:18 2017
Mount count: 22
Maximum mount count: -1
Last checked: Wed Dec 28 16:17:14 2016
Check interval: 0 (<nuser>)
Lifetime writes: 1565 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
Default directory hash: half_md4
Directory Hash Seed: 2474f801-44c2-4fe1-8809-34759b56a2fb
Journal backup: inode blocks
user@box:~$ sudo tune2fs -l /dev/md99|grep -i reserved
Reserved block count: 97673676
Reserved GDT blocks: 558
Reserved blocks uid: 0 (user root)
Reserved blocks gid: 0 (group root)
Solution change to 2% reserved blocks instead of 5%
The -m2 means 2% change that to the percentage you want.
sudo tune2fs -m2 /dev/md99
tune2fs 1.42.9 (4-Feb-2014)
Setting reserved blocks percentage to 2% (39069470 blocks)
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