RAID/LVM Root Filesystem on SuSE8.2

[Matthew Carpenter]

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Hi David,

It was obvious re-reading that first (and second) that I learned a lot
last night after writing it.

Yes, the superblock is what's important for booting from a RAID Root.
Since I'm using mdadm, the /etc/raidtab is more of a documentation than
required.  In fact, I removed it since SuSE actually uses it if it's
present.

I am familiar with building RAID into a live system.  The details were
just not all there and I had to learn a lot about what was going on
underneath.  Unfortunately, this offline hard-copy article was the only
reference to using RAID and LVM together successfully.  I read a lot
about booting from a RAID device, but not the combination.  For all I
know this article (April 04) could have been inspired by your howto.
But I think we have different philosophies about their combination.  I
believe that making raid devices from LVs hinders the flexibility of LVM
because you suddenly have two identical LVs you have to make sure are
the same size.  Growth becomes more difficult if possible.


David Bandel wrote:
<snip>

|>
|>To be safe, I also created /etc/mdadm.conf and /etc/raidtab.  I also
|>added lvm-mod and raid1 into the initrd (which were compiled as modules
|>instead of into the kernel).  SuSE allows this by adding these module
|>names into /etc/sysconfig/kernel and running mkinitrd.
|
|
| And here's the problem.
|
| Please read my raid how-to.  It describes how to convert a running
| system to raid.  Perhaps this is what you need to do.  Create your LVM
| systems with normal disks, then go from there to raid.
|
| Also, from what I've seen here, RAID _must_ be built into the kernel
| to boot raid.  You cannot boot into raid partitions using raid
| modules. At least, I've not gotten that to work.
|

I've heard this, and perhaps it's true for LVM/RAID.  I was able to get
RAID working last night with the initrd.  I found in this article that
LVM has its own "lvmcreate_initrd" command which builds the necessary
initrd.  I am planning to figure out what it could be doing differently
from my initrd.
My concern is keeping the vendor kernel so when patches are made
available, the kernel gets updated just like all the other apps.  This
is part of scalability, which is part of my MO.

|
|>Rebooting using this new entry kicks out the following error messages
|>(many lines snipped):
|>
|
|
| [many more lines snipped]
|
| When you create the raid, a superblock will be written.  You need this
done.
|
| I suspect for your setup, you'll need LVM and RAID built into the
| kernel so lvm can come up first, then the raid, then finally begin
| booting off your disks.
Possibly.  Or perhaps I need to tweak the initrd some more.  Either way,
it's obviously simpler if both are compiled into the  kernel.

- --
Matthew Carpenter
matt at eisgr.com                          http://www.eisgr.com/

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