Re: Proposed Enhancements to MD

Andreas Dilger
2004-01-13T22:18:31Z

On Jan 13, 2004 08:19 -0600, Matt Domsch wrote:
> On Mon, Jan 12, 2004 at 08:41:54PM -0700, Scott Long wrote:
> > - DDF Metadata support: Future products will use the 'DDF' on-disk
> > metadata scheme. These products will be bootable by the BIOS, but
> > must have DDF support in the OS. This will plug into the abstraction
> > mentioned above.
>
> For those unfamiliar with DDF (Disk Data Format), it is a Storage
> Networking Industry Association (SNIA) project ("Common RAID DDF
> TWG"), designed to provide a single metadata format to be used by all
> the RAID vendors (hardware and software alike). It removes vendor
> lock-in by having a metadata format that all can use, thus in theory
> you could move disks from an Adaptec hardware RAID controller to an
> LSI software RAID solution without reformatting the disks or touching
> your file systems in any way. Dell has been championing the DDF
> concept for quite a while, and is driving vendors from which we
> purchase RAID solutions to use DDF instead of their own individual
> metadata formats.
>
> I haven't seen the spec yet myself, but I'm lead to believe that
> DDF allows for multiple logical drives to be created across a single
> set of disks (e.g. a 10GB RAID1 LD and a 140GB RAID0 LD together on
> two 80GB spindles), as well as whole disks be used. It has a
> mechanism to support reconstruction checkpointing, so you don't have
> to restart a reconstruct from the beginning after a reboot, but from
> where you left off. And other useful features too that you'd expect
> in a common RAID solution.

So, why not use EVMS and/or Device Mapper to read the DDF metadata and
set up the mappings that way?

Cheers, Andreas
--
Andreas Dilger