fdisk /dev/sdb
d (delete all parts)
6
d
5
d
2
d
1
n (create new part)
p (primary)
1 (first part)
1 or return
xxx (=max cylinder/4)
n
p
2
return
yyy
n
p
3
return
zzz
n
p
4
return
return
w
reboot
fdisk -l
fdisk /dev/sdb
d (delete all parts)
6
d
5
d
2
d
1
n (create new part)
p (primary)
1 (first part)
1 or return
xxx (=max cylinder/4)
n
p
2
return
yyy
n
p
3
return
zzz
n
p
4
return
return
w
reboot
fdisk -l