unable to mkfs.btrfs ERROR: unable to open /dev/sdc: Device or resource busy

I have an old Dell PowerEdge 1950 with a LSA SAS card connecting three hard drives. I am running Ubuntu 16.04 server. When I run the following command:

sudo mkfs.btrfs -d raid6 -f /dev/sdc /dev/sdd /dev/sde

I get

btrfs-progs v4.4
See for more information.
ERROR: unable to open /dev/sdc: Device or resource busy

Drives are not mounted yet:

mount | grep /dev/sd
/dev/sda1 on / type btrfs (rw,relatime,space_cache,subvolid=257,subvol=/@)
/dev/sda1 on /home type btrfs (rw,relatime,space_cache,subvolid=258,subvol=/@home)

I have also noticed these devices don't list the file for the first partition, example /dev/sdd1, but I have partitioned successfully

sudo fdisk -l
Disk /dev/sdc: 279.4 GiB, 300000000000 bytes, 585937500 sectors
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: 0x000b958a
Device Boot Start End Sectors Size Id Type
/dev/sdc1 2048 585937499 585935452 279.4G 83 Linux
Disk /dev/sdd: 279.4 GiB, 300000000000 bytes, 585937500 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk /dev/sdb: 279.4 GiB, 300000000000 bytes, 585937500 sectors
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: 0x23bde1bc
Device Boot Start End Sectors Size Id Type
/dev/sdb1 2048 585937499 585935452 279.4G 83 Linux

Any suggestions?

Thanks, Tim

2 Answers

A possibility, that happened to me, is that the hard drive was at some point a component of a software RAID. In such case, even if "deleting" its partition table, and rebooting, there will be some persistent data in the superblock that causes the OS (CentOS 7 in my case) to recognize that and to create an entry such as /dev/md127 in the /dev directory.

Now that I want disk this just to work stand-alone, no more RAID association to it, you'll need to tell the system, such as:

# mdadm --stop /dev/md127

(You may use mdadm --detail /dev/md127 to see metadata beforehand).

After the stop, that metadata is gone, and the disk can be reused.

My own research suggests the multipath daemon is to blame. Diable that service if it exists to fix the issue. I'm having the same problem on a Dell 1950 tonight: I can format one hard drive, but not the other, despite running off a live USB.