Re: Moving root to raid, weird raid behaviour

[Wols Lists <antlists@youngman.org.uk>]

On 23/09/14 01:37, NeilBrown wrote:
> On Mon, 22 Sep 2014 19:29:46 +0100 Wols Lists
> <antlists@youngman.org.uk> wrote:
> 
>> I'm not sure if this is weird raid, stupid grub2 or incompetent
>> newbie, but whatever ... and the system is my development/test
>> system so if it gets trashed it's no disaster, but I would like
>> to understand what is going on ...
>> 
>> Old setup / = sdb2 /var = sdc2 /home = mdX (sdb3, sdc3), mirror
>> 
>> I added sdd and made a new / = mdY (sdd3, missing) mirror and
>> added sdd4 to mdX /home = mdX (sdb3 sdc3 sdd4)
>> 
>> Weirdo one - sdd4 mirrored and synced fine. Then I rebooted ... 
>> mdX = (sdb3 sdc3 missing) mdZ = (sdd4 missing missing)
> 
> You probably have something silly in your initrd which is making
> invalid assumptions. What does /etc/mdadm.conf in your
> initrd/initramfs contain?

There shouldn't be anything there. I bombed into a grub2 shell, and
mdadm.conf appeared to be the empty default. I also used ark to peer
into the initramfs file and there didn't appear to be an mdadm.conf.

But I've just had a bit of an uh-oh moment. Bear in mind I have two
/boot's (mdY/boot and sdb2/boot), and two grubs or more (sda, sdb,
sdd), I could be barking up a wrong tree. So that's my next step, try
and *make* *sure* which grub I'm working with! Too many variables...
> 
>> 
>> wtf?!?!? - oh and both of them share the same uuid. The obvious
>> (but it shouldn't make any difference?) possibility is that sdb
>> and sdc are 500Gb, partitioned identically. sdd is 1Tb, so sdd4
>> is twice the size of the other two.
>> 
>> The other weirdo is I'm trying to migrate from grub/mbr to
>> grub2/gpt. Of course that's causing me fun, but I've managed to
>> get the system booting fine from mdY. Only snag is, when I list
>> /dev, mdY isn't there! mount shows it as mounted on / but that's
>> the only place I can find it!
> 
> udev should create it.  'udevadm trigger' should cause udev to
> create device files for all devices.  That should  be done as part
> of the boot sequence. If you run "udevadm trigger" does /dev/mdX
> get created?
> 
No errors, no messages, no disk ...
> 
>> 
>> mdadm v3.2.6 kernel 3.14.14-gentoo
>> 
>> Any ideas what's going on? I've googled, but everything I find
>> looks out of date or not relevant.
> 
> "out of date or not relevant"?? You must have been looking on the 
> Internet ?!?! :-)

:-)

The search results were mostly ubuntu (I run gentoo, but so what),
grub1, I'm migrating to grub2, and any mention of root/boot got plenty
of results about not finding root and failing to boot, but absolutely
nothing about successfully booting off a root that wasn't there! Plus
they all seemed to be 2010 or earlier ...
> 
> NeilBrown
> 
Cheers,
Wol