[SOLVED] Rename mdadm device

I was having some trouble with the boot partition(s) of my RAID-1. My fstab has this as /dev/md2. When I booted from the DVD to check things, /proc/mdstat showed it as /dev/md125, not /dev/md2. I ran the following in an attempt to rename it correctly:

mdadm --stop /dev/md125
mdadm --assemble /dev/md2 --name=2 --update=name /dev/sda3 /dev/sdb3

but I got:

mdadm: Merging with already-assembled /dev/md/125

Apparently, I didn't do this right. What is the correct procedure?

Thanks

Why do you think you need to do this ?.

You're in a recovery environment, it's just a device name - mount it and check the data. Seems you already have enough problems without inventing new ones.

It is the correct procedure, albeit transient, place to store array configuration permanently is /etc/mdadm.conf. What is the status of the array after it is stopped? (cat /proc/mdstat, mdadm -D)

Originally Posted by syg00 Why do you think you need to do this ?. You're in a recovery environment, it's just a device name - mount it and check the data. Seems you already have enough problems without inventing new ones.

Hmmm, never thought of that. Maybe it would have been fine once I rebooted back to that as the actual boot drive.

Originally Posted by lvm_ It is the correct procedure, albeit transient, place to store array configuration permanently is /etc/mdadm.conf. What is the status of the array after it is stopped? (cat /proc/mdstat, mdadm -D)

In the "recovery environment" there id no mdadm.conf. On the device in question it is:

ARRAY /dev/md0 metadata=0.90 UUID=dd5f03be:1895e50c:208cdb8d:9e23b04b

So maybe syg00 is right. The thing is I've booted to recovery numerous time in the past on other RAID configred systems and never noticed a /dev/md125 before. That's what threw me off -- along with numerous posts on how to (supposedly) rename the array. Also, the RAID is initially created from the setup DVD with 'mdadm --create /dev/md0 ...' not md125, but of course, there is still no mdadm.conf on subsequent boots from the DVD. AND, the other partition was still /dev/md1, not something "made up". All this confused me.

Right now, I've temporarily restored the boot drive image to a non-RAID device to get the machine up and running for production. I will re-stage these on a RAID config very soon and I'll check to see what the devices look like when I boot from DVD.

Originally Posted by mfoley In the "recovery environment" there id no mdadm.conf.

Oh, missed that - then why bother? It doesn't affect how the device is called after the normal boot. Device name you are used to is stored in mdadm.conf, it is because it is unavailable the name has changed. But the fact that device won't stop properly still indicates an issue.

I'm trying to do tests on various aspects of this issue. I booted from the installation DVD with the only the former sda member of the RAID-1 installed. I was pretty sure I have formatted those partitions back to 82 'Linux swap' and 83 'Linux' and fdisk shows that:

$ fdisk -l /dev/sda
Disk /dev/sda: 1.82 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: ST32000542AS    
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xb2b13a31

Device     Boot    Start        End    Sectors  Size Id Type
/dev/sda1           2048   16779263   16777216    8G 82 Linux swap
/dev/sda2  *    16779264 3907029167 3890249904  1.8T 83 Linux

However, it still shows as a RAID:

cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] [multipath] 
md0 : active raid1 sda1[0]
      8388544 blocks super 1.0 [2/1] [U_]
      
unused devices: <none>

What's up with that? I did 'mdadm --stop /dev/md0', deleted /etc/mdadm.conf from /dev/sda2, and rebooted. Same thing. It's still showing md0.

Why?

Re-partitioning doesn't remove raid superblock, use 'mdadm --zero-superblock'

Originally Posted by lvm_ Re-partitioning doesn't remove raid superblock, use 'mdadm --zero-superblock'

Good to know! I'll add that to my documentation for the next.

Meanhile, I've formatted these drives to be RAID-1 members again and restored the backups. All seems to be working so I'll put this RAID back into production.