RAID 10 and Persistent Superblock

RAID 10 and Persistent Superblock

[AndyLiebman]

A "simple" question regarding RAID 10. When I make a RAID 0 on top of three 
RAID 1 arrays, should I use "persistent superblock = 1" in that top level 
array? Won't that confuse the RAID software by putting two different UUIDs on the 
drives -- one for the RAID 1 arrays and one for the RAID 0 array? 

As long as I have UUIDs for the three lower level RAID 1 arrays, I should be 
able to start those arrays with mdadm even if my device ids change. 

Then shouldn't I be able to start the top level array without a UUID -- just 
by referring to the mdX numbers? In other words, if md0, md1, md2 start, there 
shouldn't be any confusion about which are the correct devices to start up 
md3. Or am I missing something?

Appreciate your answers. 

Andy Liebman

Re: RAID 10 and Persistent Superblock

[Rechenberg, Andrew]

I have a 56-disk RAID10 and I have persistent superblocks on all of the
md devices.  I believe the RAID code is smart enough to know that a
superblock already exists and places a new superblock 'before' the other
one.

So the end of your disk should look like the following drawing:

-----------------------------------|
   DATA    |  RAID0SB  |   RAID1SB |
-----------------------------------|

When I created my RAID10 array, I believe that the superblocks were
created in this fashion.  Any RAID guru care to comment?

Regards,
Andy.


On Fri, 2003-10-31 at 10:23, AndyLiebman@aol.com wrote:
> A "simple" question regarding RAID 10. When I make a RAID 0 on top of three 
> RAID 1 arrays, should I use "persistent superblock = 1" in that top level 
> array? Won't that confuse the RAID software by putting two different UUIDs on the 
> drives -- one for the RAID 1 arrays and one for the RAID 0 array? 
> 
> As long as I have UUIDs for the three lower level RAID 1 arrays, I should be 
> able to start those arrays with mdadm even if my device ids change. 
> 
> Then shouldn't I be able to start the top level array without a UUID -- just 
> by referring to the mdX numbers? In other words, if md0, md1, md2 start, there 
> shouldn't be any confusion about which are the correct devices to start up 
> md3. Or am I missing something?
> 
> Appreciate your answers. 
> 
> Andy Liebman
> -
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
-- 

Regards,
Andrew Rechenberg
Infrastructure Team, Sherman Financial Group