I am trying to create a 4 drive raid 6 with mdadm in Ubuntu. The command I am using is

sudo mdadm --create /dev/md0 --level=6 --raid-devices=4 /dev/sdb /dev/sdc /dev/sdd /dev/sde

the error I am receiving in return is

mdadm: An option must be given to set the mode before a second device (/dev/md0) is listed

I really couldn't find much that helped me when searching google, I found one thing that suggested it had something to do with the automated email. I thought that was unnecessary so I tried to skip. Is there a way I can go back now and set that up if that's causing problems?


Make sure that a RAID is not already running by issuing the following command:

cat /proc/mdstat

if you see something like this:

Personalities : [raid1]
md0 : active raid1 sdb1[1] sda1[0]
104320 blocks [2/2] [UU]

md1 : active raid1 sdb3[1] sda3[0]
19542976 blocks [2/2] [UU]

md2 : active raid1 sdb4[1] sda4[0]
223504192 blocks [2/2] [UU]

issue the following command to stop the RAID:

sudo mdadm --stop /dev/md0

you might have to remove the existing array:

sudo mdadm --remove /dev/md0

then try building the array again:

sudo mdadm --create /dev/md0 --level=6 --raid-devices=4 /dev/sdb /dev/sdc /dev/sdd /dev/sde

Hope this helps.

| improve this answer | |
  • cat /proc/mdstat returns "Personalities: unused devices: <none>" is that what I should be seeing if it's not working? – Charles S Jun 13 '15 at 15:46
  • Well, it was my own foolish fault. I didn't realize I needed to format the drives prior to creating the raid. After doing so everything seemed to work out fine. I'm going to accept your answer as the information is correct. – Charles S Jun 13 '15 at 17:05
  • @CharlieS Glad you fixed it. Also glad you figured out you needed to format your drives. I'm going to take note of that for future as well. Have a great weekend! – Terrance Jun 13 '15 at 17:41

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