Re: Does mdadm require udev/sysfs to create imsm RAID1?

[NeilBrown <neilb@suse.de>]

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On Tue, 24 Jul 2012 17:54:08 -0700 Scott Johnson <scottej23@gmail.com> wrote:

> The question may seem strange but here's the problem I'm trying to solve.
> 
> I have setup all the servers in my environment to PXE boot and nfs
> mount an older root filesystem that is a bit aged and predates udev
> and sysfs.  It just has the /dev/ device tree.
> 
> This worked well for installing proprietary PCI highpoint 1720 raid
> drivers that aren't included in the kernel.  Then I would write my OS
> images to the drives after installing the raid driver.  However, now
> my latest hardware comes with the Intel IMSM and I don't need to use
> the pci raid anymore if I can get this on-board imsm raid to work.
> 
> I built the latest mdadm (3.2.5) and added it to my root filesystem.
> The mdadm --examine /dev/sda seems to see that the drives are
> configured but mdadm create fails and the mdadm --assemble --scan does
> nothing.  I did configure the RAID1 array in the bios.
> 
> I'm currently using an older 2.6.30 kernel, but should be new enough
> for imsm via mdadm.  If mdadm requires udev and sysfs info then I'll
> have to figure out how to include that into my root filesystem.
> 
> -bash-3.1# uname -r
> 2.6.30
> 
> -bash-3.1# mdadm -V
> mdadm - v3.2.5 - 18th May 2012
> 
> -bash-3.1# cat /proc/mdstat
> Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
> unused devices: <none>
> 
> -bash-3.1# mdadm -E /dev/sda
> mdadm: /dev/sda is not attached to Intel(R) RAID controller.
> mdadm: /dev/sda is not attached to Intel(R) RAID controller.
> /dev/sda:
>           Magic : Intel Raid ISM Cfg Sig.
>         Version : 1.1.00
>     Orig Family : 41dddea6
>          Family : 41dddea6
>      Generation : 00000035
>      Attributes : All supported
>            UUID : 64fabbb6:c0dfc0df:dc004a9e:620cffc5
>        Checksum : 242ff277 correct
>     MPB Sectors : 1
>           Disks : 2
>    RAID Devices : 1
> 
>   Disk00 Serial : Z2AFVZJZ
>           State : active
>              Id : 00020000
>     Usable Size : 625137928 (298.09 GiB 320.07 GB)
> 
> [Volume0]:
>            UUID : 83543199:fdb1493f:0f2af5ef:e2287504
>      RAID Level : 1
>         Members : 2
>           Slots : [UU]
>     Failed disk : none
>       This Slot : 0
>      Array Size : 625137664 (298.09 GiB 320.07 GB)
>    Per Dev Size : 625137928 (298.09 GiB 320.07 GB)
>   Sector Offset : 0
>     Num Stripes : 2441944
>      Chunk Size : 64 KiB
>        Reserved : 0
>   Migrate State : idle
>       Map State : normal
>     Dirty State : clean
> 
>   Disk01 Serial : Z2AFVZN8
>           State : active
>              Id : 00030000
>     Usable Size : 625137928 (298.09 GiB 320.07 GB)
> 
> -bash-3.1# mdadm --assemble --scan
> mdadm main: failed to get exclusive lock on mapfile
> mdadm: No arrays found in config file or automatically
> 
> -bash-3.1# mdadm --create /dev/md/imsm -e imsm -n 2 /dev/sda /dev/sdb
> mdadm: /dev/sda is not attached to Intel(R) RAID controller.
> mdadm: /dev/sda is not suitable for this array.
> mdadm: /dev/sdb is not attached to Intel(R) RAID controller.
> mdadm: /dev/sdb is not suitable for this array.

IMSM raid should work without udev.  It definitely does require sysfs though.

However it seems that mdadm doesn't think you have an Intel RAID controller,
so it isn't going to work for you.
You can over-ride that check using
  export IMSM_NO_PLATFORM=1

However it may be that it says  that because you don't have /sys mounted.
If you really don't (and I imagine many things would fail without /sys)
then you really need to get it mounted.

NeilBrown


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