Initial creating with a missing device

# mdadm –create /dev/md0 –level=5 –raid-devices=3 /dev/sdg /dev/sdh /dev/sdi missing

Checking the details of the newly created device

# mdadm –detail /dev/md0

/dev/md0:
Version : 1.2
Creation Time : Mon Nov 2 19:52:19 2015
Raid Level : raid5
Array Size : 7813774336 (7451.80 GiB 8001.30 GB)
Used Dev Size : 3906887168 (3725.90 GiB 4000.65 GB)
Raid Devices : 3
Total Devices : 2
Persistence : Superblock is persistent

Update Time : Tue Nov 3 00:41:28 2015
State : active, degraded
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Layout : left-symmetric
Chunk Size : 512K

Name : homenas.mytso.net:0 (local to host homenas.mytso.net)
UUID : 938a8e0a:bc9e76c9:3fe9e991:9cd690e2
Events : 723

Number Major Minor RaidDevice State
0 8 96 0 active sync /dev/sdg
1 8 112 1 active sync /dev/sdh
2 0 0 2 removed

Create config and update ramfs for booting

# mdadm –detail –scan >> /etc/mdadm/mdadm.conf
# update-initramfs -u