Is it possible to disable power supply to an USB storage device when unmounting?

costavi · 11-13-2006, 12:18 PM

I noticed a difference in the way the "unmounting" of USB storage devices is done in Linux and Windows.
Under Windows the device is detached from the filesystem and the power supply to the device is disabled, so that the device is switched off, then you can remove it.
Under Linux (at least in the major distributions), you "unmount" the device from the filesystem, but the device is still on-line, in fact you can mount it again from command line if you want, without removing and inserting it again in the USB slot.
I wonder if it is possible to make a 'Windows like' unmounting under Linux, which I think would be safer for small external 2.5'' hard drives receiving power supply from the USB bus.
Does anyone know how to do it (if possible)?

b0uncer · 11-13-2006, 12:39 PM

Quote:

Under Windows the device is detached from the filesystem and the power supply to the device is disabled, so that the device is switched off, then you can remove it.

Well, not every day

you can (or at least I was able to) try to do it and fail, in case Windows does somekind of half-paralyzing crash. But yes, now that you mention it, it seems like this is what happens. Having said that I must say I have 100% surely faced a situation (even multiple times) where a USB-mp3-player-mass-storage-cadget was unmounted (or I meant to do it that way) and after that it didn't mount -- and yes, reason was that the cadget was powerless and I had to de/re-attach it to get it mounted again. Since I found myself again in a situation where I have absolutely no USB devices around (as usual, if I happened need one) I can't try out but does it make difference if you

Code:

umount /dev/sda1

or

Code:

eject /dev/sda1

I'm not sure about this as this is probably the first time I ever think this matter from this angle; both of those do the trick of umounting the filesystem, but ejecting will cause cds, for example, pop the drive tray open which umount won't do. Probably doesn't make a difference for USB storage devices, but try out

The thing I was trying to say was yes; it should be possible.

costavi · 11-14-2006, 03:23 AM

Eventually I tried with a USB pendrive and with a USB 2.5'' hard drive. The command:

eject <devicename>

normally unmount the device

, but nothing more, the power is still on and I can remount the device without re-inserting it in the USB slot.