[gentoo-user] USB power management

[gentoo-user] USB power management

[Andrew Tselischev]

Hello list,

Recently I came into possession of an external USB hard drive. The
user's manual (obviously) stated that I should always use "safe removal
function" prior to disconnecting the hard drive. I suspect the purpose
of this is to tell the device to properly park the heads and power down,
but I don't have any idea how to do that on linux.

I tried writing '3' to /sys/bus/usb/device/.../power/autosuspend and
'auto' to /sys/.../power/control but this doesn't power down the drive.
I do hear the indicative "click" after 3 seconds (at least I think I do),
but the "PWR" led still stays on, /sys/.../power/runtime_status still
says "active" (instead of "suspended") and I can access the data on the
block device /dev/sdb, all of which suggests that the drive is still
powered on.

So, perhaps you could give me a tip on how to properly detach USB
drives or link me to an up-to-date information about the kernel's USB
subsystem.


I should mention that I'm not using any of the over-complicated DEs,
just the bare bones X server with awesomewm and a terminal emulator.

I'm currently running kernel version 3.12.6-gentoo with udev-208 and
udisks-2.1.1

Re: [gentoo-user] USB power management

[Mick]

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On Thursday 02 Jan 2014 17:16:32 Andrew Tselischev wrote:
> Hello list,
> 
> Recently I came into possession of an external USB hard drive. The
> user's manual (obviously) stated that I should always use "safe removal
> function" prior to disconnecting the hard drive. I suspect the purpose
> of this is to tell the device to properly park the heads and power down,
> but I don't have any idea how to do that on linux.

Are you sure of this, or is it just an assumption?

I would think that the "safe removal" refers to unmounting the fs so that 
nothing is writing to it at the moment you are unplugging it.  If not it will 
likely corrupt the filesystem.  So use whichever method you used to mount it 
to safely unmount it before you physically disconnect it from your PC.


> I tried writing '3' to /sys/bus/usb/device/.../power/autosuspend and
> 'auto' to /sys/.../power/control but this doesn't power down the drive.
> I do hear the indicative "click" after 3 seconds (at least I think I do),
> but the "PWR" led still stays on, /sys/.../power/runtime_status still
> says "active" (instead of "suspended") and I can access the data on the
> block device /dev/sdb, all of which suggests that the drive is still
> powered on.
> 
> So, perhaps you could give me a tip on how to properly detach USB
> drives or link me to an up-to-date information about the kernel's USB
> subsystem.
> 
> 
> I should mention that I'm not using any of the over-complicated DEs,
> just the bare bones X server with awesomewm and a terminal emulator.
> 
> I'm currently running kernel version 3.12.6-gentoo with udev-208 and
> udisks-2.1.1

So, you should be able to do something like:

 udisksctl unmount -b /dev/sdd1 (or whatever is your device recognised as)

to be able to safely unmount it.  When power is removed by physically unplugin 
it the disk will stop spinning and the head will be parked.  Also have a look 
at 'man eject'.

-- 
Regards,
Mick

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