[root@dbserver38 ~]# umount /mnt/hd2tb
umount: /mnt/hd2tb: not mounted
[root@dbserver38 ~]# mdadm --stop /dev/md0
mdadm: stopped /dev/md0
[root@dbserver38 ~]# mdadm --create --verbose /dev/md0 --level=10 --raid-devices=4 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
mdadm: layout defaults to n1
mdadm: chunk size defaults to 64K
mdadm: /dev/sda1 appears to contain an ext2fs file system
size=1953519872K mtime=Fri Sep 28 19:39:38 2018
mdadm: /dev/sda1 appears to be part of a raid array:
level=raid10 devices=4 ctime=Wed Apr 4 12:07:08 2018
mdadm: /dev/sdb1 appears to contain an ext2fs file system
size=1953519872K mtime=Wed Apr 4 18:18:58 2018
mdadm: /dev/sdb1 appears to be part of a raid array:
level=raid10 devices=4 ctime=Wed Apr 4 12:07:08 2018
mdadm: /dev/sdc1 appears to be part of a raid array:
level=raid10 devices=4 ctime=Wed Apr 4 12:07:08 2018
mdadm: /dev/sdd1 appears to be part of a raid array:
level=raid10 devices=4 ctime=Wed Apr 4 12:07:08 2018
mdadm: size set to 976759936K
Continue creating array? y
mdadm: array /dev/md0 started.
[root@dbserver38 ~]# mount -t ext4 -o rw,noatime,max_batch_time=0,nobarrier,data=writeback /dev/md0 /mnt/hd2tb