mkfs cannot open : Device or resource busy

If you met the following issue, but you found device does NOT mount or use by anything.

mkfs.xfs -i size=512 /dev/sdb1 mkfs.xfs: cannot open /dev/sdb1: Device or resource busy

mkfs.ext4 /dev/sdb1
mke2fs 1.42.7 (21-Jan-2013)
/dev/sdb1 is apparently in use by the system; will not make a filesystem here!

check lsof, and you will find that multipathd is using it.

# lsof /dev/sdb
COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
multipath 375 root   10r   BLK   8,16      0t0 7174 /dev/sdb

How to resolve it.
You can add sd* to blacklist, then restart multipathd
cat >> /etc/multipath.conf << EOF

blacklist {
        devnode "^sd[a-z]"
}

EOF

service multipathd restart