Need help creating raid array

[/RaspberryPi]

I also posted this in r/linuxquestions
So I'm trying to learn how to create a raid array with usb thumb drives on my rpi and am getting a device busy error when creating it. The command I'm running to create it is
sudo mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sdb1 /dev/sdc1 /dev/sdd1 The exact output is
mdadm: layout defaults to left-symmetric mdadm: layout defaults to left-symmetric mdadm: super1.x cannot open /dev/sdb1: Device or resource busy mdadm: ddf: Cannot use /dev/sdb1: Device or resource busy mdadm: Cannot use /dev/sdb1: It is busy mdadm: cannot open /dev/sdb1: Device or resource busy sudo dmsetup table shows no devices found. What can I do to fix this error? Thank you in advance

submitted by /u/Djcrafty
[link] [comments]

More...