Date: Tue, 1 Jun 2004 16:42:24 +0100
From: John Bradford <john@grabjohn.com>
Message-Id: <200406011542.i51FgOwk000160@81-2-122-30.bradfords.org.uk>
To: "Tvrtko A. =?iso-8859-2?q?Ur=B9ulin?=" <tvrtko.ursulin@zg.htnet.hr>,
       linux-kernel@vger.kernel.org
In-Reply-To: <200406011713.59904.tvrtko.ursulin@zg.htnet.hr>
References: <200406011713.59904.tvrtko.ursulin@zg.htnet.hr>
Subject: Re: Question about IDE disk shutdown
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1560
Lines: 37

Hi,

> Probably a trivial question for ones who know it - what IDE commands does 
> kernel issue when shutting down (which results in automatic power-off if ACPI 
> is enabled)?
> 
> According to my hard disk manual, it is absolutely recommended to put the 
> drive in STANDBY or SLEEP mode before power cut-off because in that way heads 
> are nicely parked. In that way it is guaranteed to have 300000 head 
> load/unload cycles minimum, while in other case it is just 20000 cycles.
> 
> It also explicitely states that FLUSH CACHE is not to be used for drive 
> power-off because it does not park the heads.
> 
> Looking at the source I see in ide-disk.c:
> 
> 	.gen_driver = {
> 		.shutdown	= ide_device_shutdown,
> 	},
> 
> Following that I see that ide_device_shutdown flushes the cache, and then 
> calls dev->bus->suspend(dev, PM_SUSPEND_STANDBY); which is in fact 
> generic_ide_suspend, right? There, something called REQ_PM_SUSPEND is issued 
> to the drive. As SUSPEND != STANDBY or SLEEP, I am left uncertain.
> 
> Is there a place to be worried or I am missing something? 

This kind of thing has been discussed extensively in the past.  Basically,
there are loads of broken drives which do a wide range of different things,
so following the standards doesn't necessarily work best in practice.

John.
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