linux-kernel - RE: [linux-pm] Power management for SCSI

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Message-ID: <556445368AFA1C438794ABDA8901891C09532734@USA0300MS03.na.xerox.net>
Date:	Tue, 19 Aug 2008 17:08:58 -0400
From:	"Leisner, Martin" <Martin.Leisner@...ox.com>
To:	"Alan Stern" <stern@...land.harvard.edu>
Cc:	"Oliver Neukum" <oneukum@...e.de>,
	"Linux-pm mailing list" <linux-pm@...ts.osdl.org>,
	"kernel list" <linux-kernel@...r.kernel.org>, <teheo@...ell.com>,
	<James.Bottomley@...senpartnership.com>,
	"Pavel Machek" <pavel@...e.cz>,
	"Stefan Richter" <stefanr@...6.in-berlin.de>
Subject: RE: [linux-pm] Power management for SCSI

Being able to drop power on the disk on demand is a useful concept.

We do it, but need a number of custom patches in a number of places.

When the system WANTS to access the disk, it does what is necessary to
get the disk to spin up...

I'm not sure dropping disk power in a control way should trigger a
hot-plug
event --if everyone EXPECTS it.

I'm just looking for a more generic way to enable this...I'm going to be
looking a 2.6.26/27 for this soon...

marty

>   -----Original Message-----
>   From: Alan Stern [mailto:stern@...land.harvard.edu]
>   Sent: Wednesday, August 13, 2008 4:39 PM
>   To: Leisner, Martin
>   Cc: Oliver Neukum; Linux-pm mailing list; kernel list;
teheo@...ell.com;
>   James.Bottomley@...senpartnership.com; Pavel Machek; Stefan Richter
>   Subject: RE: [linux-pm] Power management for SCSI
>   
>   On Wed, 13 Aug 2008, Leisner, Martin wrote:
>   
>   > Regarding these scsi suspend patches, there's a general
>   > problem to drop power on disk devices on a running system.
>   > I discussed it in:
>   >
>   > http://www.gossamer-threads.com/lists/linux/kernel/811598
>   
>   There's a much worse problem which that thread completely ignored:
>   
>   When you turn off power to a disk device, to the system it looks
like a
>   hot-unplug event.  Any mounted filesystems or memory mappings on
that
>   disk will be lost.
>   
>   Alan Stern

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