USB NTFS external disk spinning up every minute

[vicuvic]

Hello folks

I've installed a Debian 8.6 and configured Samba sharing a NTFS external drive over USB.
For some reason every minute the disk is spinned up, moving from standby state to active/idle and after few seconds moving back standby, and repeating this cycle every minute.
I checked with iotop but there is nothing writing on that disk.
Enabled the debug with: echo 1 > /proc/sys/vm/block_dump and checked dmesg, but nothing
Configure the APM to 127:
setting Advanced Power Management level to 0x7f (127)
APM_level = 127

Standby timer to 15 min:
hdparm -S 180 /dev/sdc1

/dev/sdc1:
setting standby to 180 (15 minutes)

Any clue what else to check?

Thanks
V.

[vicuvic]

Modified the two command pointing to /dev/sdc - no results
Stopped samba .. still going up and down

I'll check further

Thanks