[lug] Convert swap from raid0 to raid1

[Nate Duehr]

On Jul 26, 2007, at 1:42 AM, dio2002 at indra.com wrote:

> So the question is where is that raid level metadata stored. in the
> superblock?  because it ignores whatever you put in mdadm.conf.
>
Yes... but...

Depending on distro implementation, it may not be used.

 From 2006 Debian discussions (it didn't take me too long to find  
this, because I was reading some of this stuff at the time, and  
amazed at the complexity)...

http://lists.debian.org/debian-user/2006/11/msg01048.html

That message and all the links from it referencing other stuff, just  
to describe why Debian wasn't going to use the mdrun "magic" that  
read things and tried to figure out what was going on only from  
superblock data... I assume other distros have had or done similar  
things on and off over time.

> And along the same lines, which boot scripts create the arrays and  
> where
> is the metadata it uses to create them stored.  it has to be  
> persistent
> between boots.  and i don't think it's getting it from mdadm.conf.

As you can see from the above, it might have needed mdadm.conf  
originally to write it to the superblocks, or various "magic" may  
have been used to determine what to write to the superblocks, or...  
well, it's getting into "chicken and egg" stuff in the overall design  
of it, really.

Veritas (commercial stuff) always stores ALL of the pertinent data on  
disk... the kernel module just immediately goes out and finds all  
this junk on all disks at every boot, similar to the retired mdrun in  
Martin's message above... but that doesn't mean every distro  
implements it the same way...

All these whacky differences can drive you crazy trying to track  
them, like the kernel itself, and most successful long-term linux  
software packages, it's constantly morphing into different things,

And at least this stuff I can get my head around.  I attempted to  
track some Perl internals discussions on their mailing lists once,  
and thought my head was going to explode.

--
Nate Duehr
nate at natetech.com