# dd if=/dev/zero of=/dev/sdb bs=1024 count=5000
# fdisk /dev/sdb
# fdisk -l /dev/sdb
Disk /dev/sdb: 232.9 GiB, 250000000000 bytes, 488281250 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: 0x35c9935e

Device     Boot    Start       End   Sectors   Size Id Type
/dev/sdb1  *        2048    206847    204800   100M 83 Linux
/dev/sdb2         206848   4401151   4194304     2G 82 Linux swap / Solaris
/dev/sdb3        4401152  16984063  12582912     6G 83 Linux
/dev/sdb4       16984064 488281249 471297186 224.7G 83 Linux

# mdadm --create --raid-devices=2 --level=raid1 /dev/md0 /dev/sdb3 missing
# mdadm --create --raid-devices=2 --level=raid1 /dev/md1 /dev/sdb4 missing

# mkfs.ext2 /dev/sdb1 
# mkreiserfs /dev/md0