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.
DDF is quickly becoming important to RAID and system vendors, and I
welcome Adaptec's work to implement DDF support on Linux.
Thanks,
Matt
--
Matt Domsch
Sr. Software Engineer, Lead Engineer
Dell Linux Solutions http://www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com
Matt Domsch wrote:
> DDF is quickly becoming important to RAID and system vendors, and I
> welcome Adaptec's work to implement DDF support on Linux.
Fully agreed, the days of vendor-specific metadata formats need to be
numbered (with a small number). Speaking a customer with a CMD
FC-to-SCSI RAID controller, which used to be dual-redundant but is now
single (because of a dead unit), we are not looking forward to the day
when the remaining controller dies and we lose all the data on the array
due to a forced metadata format change.
However, given that this will not likely be 2.6 material until after
it's built and tested in 2.7 and then backported, it doesn't seem to
make any sense to me to build any of this on top of the MD subsystem at
all (see other replies about using DM instead). Additionally, it also
does not seem to make any sense to build any of the DDF
reading/writing/management in the kernel _at all_. There is no advantage
to it being there once initramfs is a standard part of the boot process,
so all of this should be done is userspace and just communicated into
the kernel to tell it what logical devices to construct using which DM
modules.
Matt Domsch wrote:
> 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
Me either. Any idea if there will be a public comment period, or is the
spec "locked" into 1.0 when it's released in a month or so?
Jeff
On Tue, Jan 13, 2004 at 01:19:56PM -0500, Jeff Garzik wrote:
> Matt Domsch wrote:
> > 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
>
>
> Me either. Any idea if there will be a public comment period, or is the
> spec "locked" into 1.0 when it's released in a month or so?
As it happens, Bill Dawkins of Dell is the DDF committee chair at
SNIA. Here's what he's told me:
The current draft of the DDF specification is available for review
to any member of SNIA. This is a "Work in Progress" draft. Anyone in a
member company can go to http://www.snia.org and sign up for web access. They
will then have to sign up for the DDF Technical Working Group.
Acceptance to the DDF TWG is automatic and the current documents are
available there.
(As Dell is a member, I signed up for the DDF TWG as an observer.
Other companies are also on the member list, including Sistina, so
Jeff you may be able to get a Sistina collegue to mail you a copy.
http://www.snia.org/about/member_list has the list of member
companies. - Matt)
For people and companies who are not members of SNIA, I am writing to
the SNIA Technical Director to see if I can release copies of the
draft spec now. I'll let you know when I get a response.
As for the timeline, we have a face to face meeting of the DDF TWG
next Tuesday and it is our intent to vote on releasing the
specification as a "Trial Use" specification for public review and
comment. If the vote is affirmative, the SNIA Technical Council will
have to meet to determine when and if to release the "Trial Use"
specification. This may take a few months, so we are probably looking
at March for full release. Feel free to share this information with
your Linux contacts.
So, for now, if you're in SNIA, you can get access to the draft spec,
and in a few months the draft spec should be publicly available.
Thanks,
Matt
--
Matt Domsch
Sr. Software Engineer, Lead Engineer
Dell Linux Solutions http://www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com
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
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/
On Jan 13, 2004 10:13 -0700, Andreas Dilger wrote:
> So, why not use EVMS and/or Device Mapper to read the DDF metadata and
> set up the mappings that way?
PS - outgoing email was delayed, this has already been covered. Sorry.
Cheers, Andreas
--
Andreas Dilger
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/