RAID autodetection not working when booting with initramfs

RAID autodetection not working when booting with initramfs

[Dimitris Zilaskos]

 	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 ?

 	TIA,

--
============================================================================

Dimitris Zilaskos

Department of Physics @ Aristotle University of Thessaloniki , Greece
PGP key : http://tassadar.physics.auth.gr/~dzila/pgp_public_key.asc
 	  http://egnatia.ee.auth.gr/~dzila/pgp_public_key.asc
MD5sum  : de2bd8f73d545f0e4caf3096894ad83f  pgp_public_key.asc
============================================================================

Re: RAID autodetection not working when booting with initramfs

[Neil Brown]

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

Re: RAID autodetection not working when booting with initramfs

[Dimitris Zilaskos]

> 	/*
> 	 * 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.
>

 	Thank you , raidautorun did the trick. I am trying to build an 
initramfs as much generic as possible to be used with hundreds of systems, 
so doing a custom image for every possible raid combination is really not 
an options compared to autodetection.

 	Thnx again,

--
============================================================================

Dimitris Zilaskos

Department of Physics @ Aristotle University of Thessaloniki , Greece
PGP key : http://tassadar.physics.auth.gr/~dzila/pgp_public_key.asc
 	  http://egnatia.ee.auth.gr/~dzila/pgp_public_key.asc
MD5sum  : de2bd8f73d545f0e4caf3096894ad83f  pgp_public_key.asc
============================================================================