partition md raid?

partition md raid?

[William Thompson]

Is this possible (w/o using lvm)

Re: partition md raid?

[Jakob Oestergaard]

On Wed, Jun 19, 2002 at 10:36:11AM -0400, William Thompson wrote:
> Is this possible (w/o using lvm)

Not currently, and as far as I remember, there is no good reason behind
it (except that no-one's done it  ;)

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:

Re: partition md raid?

[Neil Brown]

On Wednesday June 19, wt@electro-mechanical.com wrote:
> Is this possible (w/o using lvm)

Yes, but you need a patch...
http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
 2.4.19-pre8 section
      patch-Z-MdLocks
            Improve locking of MD related structure, particularly when reconfiguring 
      patch-a-RaidSplit
            Split raid requests that span chunks 
      patch-b-MdPart
            Enable partitioning of MD devices 
      patch-c-MdpMajor
            Define a static major number for mdp - partitioned md 

These patches should make the first 16 devices partitionable.
Without patch-c-MdpMajor, a free major number is allocated (usually
254, but no guarantees) and you have to either:
 - have a script which finds the number from /proc/devices and makes
   all the /dev entries, or
 - use devfs

With patch-c-MdpMajor, Major number "60" (LOCAL/EXPERIMENTAL USE) is
allocated for the partitioned md devices.

I use this in production.  I have two system discs (sda and sdb, or
hda and hdc) which are mirrored together as whole devices, and then
this is partitioned:
   mda1 == root
   mda2 == swap
   mda3 == other...

Getting lilo to cope was interesting, but it works.

NeilBrown

Re: partition md raid?

[Jakob Oestergaard]

On Fri, Jun 21, 2002 at 12:51:40PM +1000, Neil Brown wrote:
> On Wednesday June 19, wt@electro-mechanical.com wrote:
> > Is this possible (w/o using lvm)
> 
> Yes, but you need a patch...
...

Any plans for getting this into the kernel Neil ?

I get quite a few questions from people who either do not understand
that you cannot partition md devices (and do various rather
involuntarily interesting setups because of that), or people who
understand the limitation but not the reason behind it.

Thinking about it, I don't know the reason   ;)

It's really a functionality that a lot of people feel naturally is
there, and I can't blame them.

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:

Re: partition md raid?

[Neil Brown]

On Friday June 21, jakob@unthought.net wrote:
> On Fri, Jun 21, 2002 at 12:51:40PM +1000, Neil Brown wrote:
> > On Wednesday June 19, wt@electro-mechanical.com wrote:
> > > Is this possible (w/o using lvm)
> > 
> > Yes, but you need a patch...
> ...
> 
> Any plans for getting this into the kernel Neil ?

I've been hanging out for 2.4.19 to be released.  Then I hope to
submit some of the changes that recently went into 2.5 (which sort out
the locking) and then the partitioning.

I suspect the functionality will end up in 2.5 one day, but I'm not
sure how and I'm not going to push it until (unless) the block_dev
layer settles down.

NeilBrown