From: Neil Brown <neilb@suse.de>
To: Dimitris Zilaskos <dzila@tassadar.physics.auth.gr>
Date: Mon, 30 Jan 2006 10:33:15 +1100
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Message-ID: <17373.20667.838469.977966@cse.unsw.edu.au>
Cc: linux-kernel@vger.kernel.org
Subject: Re: RAID autodetection not working when booting with initramfs
In-Reply-To: message from Dimitris Zilaskos on Monday January 30
References: <Pine.LNX.4.64.0601300103110.2016@tassadar.physics.auth.gr>
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On Monday January 30, dzila@tassadar.physics.auth.gr wrote:
> 
>  	Hi ,
> 
>  	I am building a diskless system with 2.6.15.1 kernel. Eveyrthing is built 
> in the kernel ( no modules). It is booting with the help of pxelinux and 
> then proceeds to nfsmount its root filesystem etc.The system has a raid1 
> array on two scsi disks.
>  	Recently I added an initramfs image to the boot procedure (append 
> initrd=initramfs.img) for some tests. Since then the raid array is not 
> autodetected (with identical kernel). If I remove the initramfs line and 
> reboot , the array is autodetected. When I am using initramfs I can 
> manually activate it using mdadm.
> 
>  	Is this by design or something is wrong ?

To quote from init/main.c:
	/*
	 * check if there is an early userspace init.  If yes, let it do all
	 * the work
	 */

So yes, it is by design.  Assembling arrays with mdadm gives you a
lot more control than the kernel-autodetect so as you have an
initramfs, it is a good idea to make use of it.

If you *really* want to use the autodetect functionality, you can look
around for a program called 'raidautorun'.  It does triggers the
autodetect function from userspace.

NeilBrown
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