I successfully created a RAID (mirroring) by utilizing mdadm. However, I must run the following commands after each boot:
mdadm --stop --scan // to stop /dev/md127 - I don't know where the number 127 even comes from
mdadm --assemble --scan // to start /dev/md0
What am I doing wrong/why do I need to run these commands at boot? What is the right way to auto-start RAID with each (re)boot?
NB: You either need to be logged in as root, or use sudo to do all this...
If the file does not even exist, paste the following into the new, empty file:
# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#
DEVICE partitions
# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes
# automatically tag new arrays as belonging to the local system
HOMEHOST <system>
# instruct the monitoring daemon where to send mail alerts
MAILADDR root
# definitions of existing MD arrays
Save the file
Run the following command to add a reference to your array config at the end of the file:
mdadm --detail --scan >> /etc/mdadm/mdadm.conf
This should add a line like the following to the end of mdadm.conf:
ARRAY /dev/md0 level=raid5 num-devices=3 metadata=00.90 UUID=a44a52e4:0211e47f:f15bce44:817d167c
If the mdadm command has added any other stuff above the ARRAY line, remove it. For example, on one of my machines, the command returns 'mdadm: metadata format 00.90 unknown, ignored.' before the ARRAY line.
Your array should now auto-build on boot and thus you can add an entry to /etc/fstab to mount it (if it's not already there)
I realize this is an older question, but I had a frustrating time with this on the 32-bit version of Ubuntu Server 12.04.
Running mdadm --detail --scan >> /etc/mdadm/mdadm.conf appended the line
ARRAY /dev/md0 metadata=1.2 name=ubuntu:0 UUID=a8a570c6:96f61865:05abe131:5c2e2f7e
After a reboot I could never see /dev/md0. Running the mdadm --detail --scan again (without putting the result in a file) I would see
ARRAY /dev/md/ubuntu:0 metadata=1.2 name=ubuntu:0 UUID=a8a570c6:96f61865:05abe131:5c2e2f7e
and manually mounting /dev/md/ubuntu:0 would work. In the end, that was what I put in the fstab file too.
I am not sure what I got wrong, if this is how it works in Ubuntu 12.04, or if this is a bad practice. Just wanted to share what worked for me.
I had this problem on my Raspberry Pi 2 running Raspbian GNU/Linux 8 (jessie). I had a RAID array on /dev/sda1 and /dev/sdb1 which failed to assemble at boot. I had in my /etc/mdadm/mdadm.conf file the entry
ARRAY /dev/md/0 metadata=1.2 UUID=53454954:4044eb66:9169d1ed:40905643 name=raspberrypi:0
(your numbers will be different; see other answers on how to get this.)
I had in my /etc/fstab file the entry
/dev/md0 /data ext4 defaults 0 0
(and of course /data indeed existed)
Like the OP, I could assemble and mount the RAID array by hand after boot, but I could not get it to happen automatically during boot despite apparently correctly setting it up.
I was able to solve the problem as follows. I investigated the script at /etc/init.d/mdadm-raid and inserted a line of debug code
ls /dev > /home/pi/devices.txt
Rebooting and checking this file I learned that devices /dev/sda and /dev/sdb existed at the time the mdadm-raid initialization happened, but the partitions /dev/sda1 and /dev/sdb1 were missing. I edited the /etc/init.d/mdadm-raid file and inserted the line
partprobe
after the header (i.e. after the ### END INIT INFO but before the script begins). This caused the partitions to be detected and so the mdadm-raid script was able to assemble the RAID array, resolving the problem. Hope this helps someone!
sudo mdadm -Es >> /etc/mdadm/mdadm.conf
Now edit lines added to /etc/mdadm/mdadm.conf in the following way. Delete everything, but the basic parts. It should look like
ARRAY /dev/md5 UUID=031cea92:50a7a28c:6b077fe7:8817092a
ARRAY /dev/md6 UUID=53454954:4044eb66:9169d1ed:40905643
Note: you can choose X in mdX to your convenience.
Now reboot
sudo update-initramfs -u
sudo reboot
EDIT: command corrected.
On Debian wheezy one more step is required:
in /etc/default/mdadm set autostart from false to true
#AUTOSTART: # should mdadm start arrays listed in /etc/mdadm/mdadm.conf automatically # during boot? AUTOSTART=true
Also I had to use mdadm -Es >>/etc/mdadm/mdadm.conf instead of the --scan option, as that did not work for me.
Having the Raspberry Pi 3, adding the rootdelay=5 to the /boot/cmdline.txt solved this problem for me.
The credit goes here.
I have been fighting with this on Raspbian using a couple of external USB HDD's on a Raspberry Pi. I had to mess with the start order of services to make sure that mdadm-raid started after the USB drives were recognised by udev but before checkfs.sh (which checks filesystems at boot time). If mdadm-raid started too early, the drives were not available and therefore the array was not assembled. That meant that fsck subsequently failed and the boot process dropped out to a maintenance prompt (because the raid array is required for other services).
Modifying boot dependencies to start mdadm-raid after checkroot.sh but before checkfs.sh and running update-rc.d mdadm-raid defaults, followed by update-initramfs -uv -k `uname -r` (note backticks around uname) fixed it (finally). For me, anyway, YMMV.
I tried with
mdadm --create /dev/md/abcdef ...
I see the softlink /dev/md/abcdef persisting on reboots and if need be access the device through soft link.
Is it a acceptable solution ?
