[PROBLEM] which device is my USB HDD?

[mmontev]

bought a new Samsung M3 1tb usb HDD.
connected to the Pi. Powered up, everithing OK. The disk was recognized, mounted and samba shared automatically. I can write read and delete. Great.

I wanted to format the drive to ext4, for better peformance. I stopped samba, ok.
But I couldn't find which devide the drive is. Here is what I get:

fidsk:

Terminal

root@xbian:/dev# fdisk -l

Disk /dev/mmcblk0: 3947 MB, 3947888640 bytes
4 heads, 16 sectors/track, 120480 cylinders, total 7710720 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 identifier: 0x000f06a6

Device Boot Start End Blocks Id System
/dev/mmcblk0p1 2048 71679 34816 c W95 FAT32 (LBA)
/dev/mmcblk0p2 71680 7710719 3819520 83 Linux

mount:

Terminal

root@xbian:/dev# mount -l
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
udev on /dev type devtmpfs (rw,relatime,size=10240k,nr_inodes=47789,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620)
tmpfs on /run type tmpfs (rw,nosuid,noatime)
/dev/mmcblk0p2 on / type btrfs (rw,noatime,thread_pool=1,compress=lzo,ssd,space_cache,autodefrag) [xbian-root-btrfs]
none on /sys/kernel/debug type debugfs (rw,relatime)
none on /sys/kernel/security type securityfs (rw,relatime)
none on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k)
none on /run/shm type tmpfs (rw,nosuid,nodev,relatime)
none on /run/user type tmpfs (rw,nosuid,nodev,noexec,relatime,size=102400k,mode=755)
/dev/mmcblk0p1 on /boot type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=ascii,shortname=mixed,​errors=remount-ro)
/dev/mmcblk0p2 on /home type btrfs (rw,noatime,thread_pool=1,compress=lzo,ssd,space_cache,autodefrag) [xbian-root-btrfs]

df:

Terminal

root@xbian:/dev# df -h
Filesystem Size Used Avail Use% Mounted on
rootfs 3.7G 2.2G 1.3G 65% /
udev 10M 4.0K 10M 1% /dev
tmpfs 189M 172K 189M 1% /run
/dev/mmcblk0p2 3.7G 2.2G 1.3G 65% /
none 5.0M 0 5.0M 0% /run/lock
none 189M 0 189M 0% /run/shm
none 100M 0 100M 0% /run/user
/dev/mmcblk0p1 34M 13M 22M 37% /boot
/dev/mmcblk0p2 3.7G 2.2G 1.3G 65% /home

I see the drive mounted in:
/media/SAMSUNG-D680D17280D15997 (or /media/usb0).
It's alive. I can use it. But I can't find which device it is.
Any help? How it is supposed to format the disk?

Thanks