Acho que você esqueceu de executar o comando resize2fs
# mdadm --detail /dev/md0
/dev/md0:
Version : 0.90
Creation Time : Sun Jul 21 23:50:49 2013
Raid Level : raid6
Array Size : 62914368 (60.00 GiB 64.42 GB)
Used Dev Size : 20971456 (20.00 GiB 21.47 GB)
Raid Devices : 5
Total Devices : 5
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Mon Jul 22 00:04:43 2013
State : clean
Active Devices : 5
Working Devices : 5
Failed Devices : 0
Spare Devices : 0
Chunk Size : 64K
UUID : c0a5733d:46d5dd5e:b24ac321:6c547228
Events : 0.13992
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
2 8 48 2 active sync /dev/sdd
3 8 64 3 active sync /dev/sde
4 8 80 4 active sync /dev/sdf
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda2 39G 1.6G 35G 5% /
/dev/sda1 494M 23M 446M 5% /boot
tmpfs 500M 0 500M 0% /dev/shm
/dev/md0 60G 188M 59G 1% /raid6
# resize2fs /dev/md0
resize2fs 1.39 (29-May-2006)
Filesystem at /dev/md0 is mounted on /raid6; on-line resizing required
Performing an on-line resize of /dev/md0 to 20971456 (4k) blocks.
The filesystem on /dev/md0 is now 20971456 blocks long.
# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda2 39G 1.6G 35G 5% /
/dev/sda1 494M 23M 446M 5% /boot
tmpfs 500M 0 500M 0% /dev/shm
/dev/md0 79G 192M 79G 1% /raid6
# mdadm --detail /dev/md0
/dev/md0:
Version : 0.90
Creation Time : Sun Jul 21 23:50:49 2013
Raid Level : raid6
Array Size : 83885824 (80.00 GiB 85.90 GB)
Used Dev Size : 20971456 (20.00 GiB 21.47 GB)
Raid Devices : 6
Total Devices : 6
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Mon Jul 22 00:04:43 2013
State : clean
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0
Chunk Size : 64K
UUID : c0a5733d:46d5dd5e:b24ac321:6c547228
Events : 0.13992
Number Major Minor RaidDevice State
0 8 16 0 active sync /dev/sdb
1 8 32 1 active sync /dev/sdc
2 8 48 2 active sync /dev/sdd
3 8 64 3 active sync /dev/sde
4 8 80 4 active sync /dev/sdf
5 8 96 5 active sync /dev/sdg
P.S. Vou sugerir desmontar / dev / md127 antes de redimensionar a operação