Re: RFC - new raid superblock layout for md driver

From: Doug Ledford (dledford@redhat.com)
Date: Thu Nov 21 2002 - 16:55:09 EST


On Thu, Nov 21, 2002 at 02:53:23PM -0600, Kevin Corry wrote:
>
> LVM doesn't handle the filesystem resizing, the filesystem tools do. The only
> thing you need is something in user-space to ensure the correct ordering. For
> an expand, the MD device must be expanded first. When that is complete,
> resizefs is called to expand the filesystem.
>
> MD currently doesn't allow resize of RAID 0, 4 or 5, because expanding
> striped devices is way ugly.

MD doesn't, raidreconf does but not online.

> If it was determined to be possible, the MD
> driver may need additional support to allow online resize.

Yes, it would. It's not impossible, just difficult.

> But it is just as
> easy to add this support to MD rather than have to merge MD and DM.

Well, merging the two would actually be rather a simple task I think since
you would still keep each md mode a separate module, the only difference
might be some inter-communication call backs between LVM and MD, but even
those aren't necessarily required. The prime benefit I would see from
making the two into one is being able to integrate all the disparate
superblocks into a single superblock format that helps to avoid any
possible startup errors between the different logical mapping levels.

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  
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