Re: multi-hosting support for carrier grade Linux

[Paul Clements <paul.clements@steeleye.com>]

Dave Jiang wrote:
> I'm attempting to implement multihost support of the MD for environments
> such as carrier grade Linux. Multihost support allows the RAID array to
> be claimed by a particular host via a unique ID (unique SCSI host ID,
> FibreChannel WWN, or geographical address of a chassis blade. That way
> another host that can access the disks do not claim the same disks that
> are used by the RAID array. 

Why not just use SCSI reservations?

> I would like to store a 64bit unique ID on the
> superblock of the device. The least intrusive way IMHO to do this is
> implementing the feature via the management app such as mdadm in
> userland. However, it seems that after I instruct the kernel to create the MD array via mdadm, the kernel starts out with a blank superblock and clobbers the

If you write a valid superblock to the disk and then assemble the array, 
the superblock doesn't get clobbered.

> data I have stored on the superblock via mdadm. Would it be acceptable
> to modify the kernel such that the unique ID info is preserved during
> the creation of the superblock by the kernel? Example patch follows:

As for adding additional fields to the various superblock formats, you'd 
have to ask Neil if he's open to that.

--
Paul