-----Original Message-----
From: FDi [mailto:fld@r00t3d.com]
Sent: Saturday, May 28, 2011 10:14 AM
To: Jiang, Dave
Cc: linux-raid@vger.kernel.org
Subject: Re: creating degraded raid1 with imsm metadata

On Thu, May 26, 2011 at 09:40:16AM -0700, Jiang, Dave wrote:

quoted

quoted

-----Original Message-----
From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
owner@vger.kernel.org] On Behalf Of FDi
Sent: Thursday, May 26, 2011 12:43 AM
To: linux-raid@vger.kernel.org
Subject: creating degraded raid1 with imsm metadata

Hello *,

Since Intel's Matrix Storage Manager option ROM doesn't support
creating of degraded arrays I was wondering if I could use mdadm to
make one? I had a very hard time finding documentation about how
mdadm is supposed to work with imsm.

The plan is to make a 2x1TB raid1 with one device missing and then
later add the other disk in once all the data has been copied to the
degraded array. So a typical raid1 migration scenario, which Intel
oddly enough doesn't seem to support with their option ROM.

Not sure if that's possible but have you looked at the Linux RAID wiki on

IMSM information?

quoted

https://raid.wiki.kernel.org/index.php/RAID_setup#External_Metadata

I wasn't able to figure out how to do what I wanted based on the wiki, but
after lots of googling I found the exact commands:

mdadm --create --force -v -e imsm --level=container -n 1 /dev/md/imsm
/dev/sdb

mdadm --create -v --level raid1 -n 2 /dev/md/myraid /dev/sdb missing

However I also learned that these commands have to be done on the target
machine while its running with RAID mode selected from BIOS. Otherwise
you will get this warning:

mdadm: imsm unable to enumerate platform support
    array may not be compatible with hardware/firmware
	 Continue creating array?

And indeed if that warning is displayed during the create, Intel's option rom
won't see a working array on the device. I'm kinda curious why is this exactly?
What kind of information mdadm uses from the controller running in RAID
mode?

It queries the table exported by the OROM regarding the capabilities of the OROM. Limits are checked such as chunk size, leve, number of devices and etc. This ensures that the OROM can recognize the RAID volume you created on Linux. You can also bypass the warning by doing: "export IMSM_NO_PLATFORM=1"
 

When I created my array on the target machine using the commands from
above it worked correctly and Intel option rom saw the array and was able to
boot from the MBR I installed on the array as a test. Haven't tested rebuilding
yet.