mdadm: cannot open /dev/md/0: No such file or directory

fakie_flip · 01-10-2013, 04:12 AM

I had just created an mdadm raid and installed Linux Mint to it. I've seen this error about /dev/md/0 a few times. I have a:

/dev/md0
and
/dev/md0p1 (had to create or Linux Mints installer would not install to the raid)

So I went to generate an /etc/mdadm/mdadm.conf file with mdadm --detail --scan, but I wanted to check the output first before redirecting it to the conf file.

Code:

bullshark@mint /etc/mdadm $ sudo /sbin/mdadm --detail --scan
sudo: unable to resolve host mint
mdadm: cannot open /dev/md/0: No such file or directory

I checked for an existing mdadm.conf. First glance, I thought it was an example and all commented out. Second glance, I found out it wasn't and it contained the line:

Code:

ARRAY /dev/md/0 metadata=1.2 UUID=a193044d:832a36d7:990196e7:a143ef21 name=mint:0

So I thought I had found the source of the /dev/md/0 error. I made a backup and then blanked out the file. I ran the above command again. It is still looking for a /dev/md/0. I have no idea why, or if that file was to exist, why it would.

smallpond · 01-10-2013, 05:42 PM

Looks like the hostname was not the same when the array was created as when you later try to assemble it. This is one of those "helpful" features that protects you from doing what you want to do. See the HOMEHOST section of the man page for mdadm.conf. Use mdadm to update the name when you assemble the array.

/dev/md0p1 typically means you didn't partition the disks before creating the RAID, which means the disks don't have labels. I like to always create the RAID on partitions but either way will work.

/dev/md/0 should be a symbolic link to /dev/md0 (or possibly to /dev/md0p1). The mdadm scan is getting the UUID and name information from the RAID superblock. It should not rewrite the mdadm.conf file unless you redirect the command output.