dm-raid and resizing

[Lennart Sorensen]

On Sat, Sep 28, 2013 at 05:32:38PM -0400, Kevin Cozens wrote:
> On 13-09-13 01:26 PM, Tyler Aviss wrote:
> >I recently upgraded a couple of RAID 2TB drives to some 3TB drives using the
> >format
> >Shutdown, pull old drive 1, start degraded
> >Add new drive 1 to RAID, wait for sync/rebuild
> >Shutdown, pull old drive 2, add new drive 2 to RAID, wait for sync/rebuild
> [snip]
> >However, for whatever reason, I can't grow to the full partition size.
> [snip]
> >Any ideas why it won't use the full capacity?
> 
> That's an interesting approach to upgrading the drives. I hadn't
> thought of that. I have a pair of 250G drives that are close to
> capacity. I bought some
> 1TB drives to replace my current drives.
> 
> Have other people tried this approach for moving to bigger drives in
> a RAID 1 configuration? Is it possible to use gparted to change the
> partition sizes after rebuild process or does it clone information
> that makes the system think the new drives are only as large as the
> original drives?

Well there are 3 types of md raid superblock.  Some put the superblock
at the end, some at the begining, and some at 4k from the begining.

I believe the one that is at the end causes a hassle when you want to
resize the device.  The other two are simple to deal with.

The one at the end has the advantage that you can mount a single device
from a raid 1 without needing any md raid knowledge since the data is
all where it would be expected to be.

-- 
Len Sorensen
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