[kwlug-disc] powering Seagate USB external disk off and on from Linux?

[D. Hugh Redelmeier]

I want to use a cheap external HDD for backups.  I want the drive to be 
off when not in use but I don't want to be required to plug or unplug the 
drive to turn it on.

Is there a way for a script to turn off a disk so it really is off enough 
and subsequently turn it on again?


- consumer HDDs have ridiculously low power-on lifetimes, at least 
  according to their specifications

- so I want my backup software to power the drive on before use and 
  off after use.

- [may be relevant] Seagate external drive controllers have a flaw: to be 
  fast, you want to use UAS (USB Attached SCSI) but the controller won't 
  pass SAT commands in this mode.  You need to tell the driver that the 
  drive has a "quirk" to lock in usb-storage mode.  
  <https://www.smartmontools.org/wiki/SAT-with-UAS-Linux>

Just unmounting all partitions of an HDD does not seem to cause it to spin 
down.  The drive still makes noise and is warm, even hours later.

Turning off the drive, using Gnome's Disks or (untested) udisksctl(1), 
does stop the drive.  But I don't know how to subsequently turn it on via 
a program.  For example, Gnome Disks doesn't see the drive once it has 
been turned off.  The way I know to turn on the drive is to physically 
unplug the USB cable and plug it in again.