Re: Using mdadm instead of dmraid for BIOS-RAID root volume

[Martin Wilck <mwilck@arcor.de>]

On 10/11/2013 03:03 PM, Brian Candler wrote:
> On 08/10/2013 19:36, Martin Wilck wrote:
>> On 10/08/2013 04:19 PM, Brian Candler wrote:
>>>   > Anyway, I'm not so worried about having broken this machine, as it
>>> needed a reinstall anyway, but I do wonder what would have been the
>>> correct way to get mdraid instead of dmraid at boot time for this root
>>> volume?
>>>
>>> After some more searching, it looks like the udev rules were nobbled to
>>> disable this in
>>> https://bugs.launchpad.net/ubuntu/+source/mdadm/+bug/1030292
>>>
>>> A possible way to re-enable is here:
>>> https://bugs.launchpad.net/ubuntu/+source/mdadm/+bug/1054948/comments/9
>>>
>>> I'm a bit concerned about the issues around clean shutdown, and hence
>>> whether is really production-ready yet.
>> In general, this works. I have seen it work with CentOS, Fedora, and
>> various SUSE distributions.
> FWIW, I found problems on stock CentOS 6.4.
> 
> I had created two RAID volumes within the BIOS:
> "BOOT" (4GB)
> "LVM" (rest of disk)
> 
> These are correctly detected and come up as md0 (container), md125 
> (BOOT), md126 (LVM). In a previous install using Debian I had set these 
> up as ext4 and LVM respectively.
> 
> In the CentOS graphical installer, they are shown as:
> 
> V Hard Drives
>      md125    4096    ext4
>      md126    902246 vg   Physical volume (LVM)
> 
> (md0 is not shown)
> 
> Problem: if I double-click on md125, or select md125 and click Edit..., 
> nothing happens. Therefore I cannot mark it as being used for the /boot 
> filesystem.
> 
> However, if I double-click on md126, it correctly pops up "You cannot 
> edit this drive: This device is part of the LVM volume group 'vg'."
> 
> Then if I delete all the logical volumes, and the volume group, I 
> expected to be able to edit md126 - but I can't. Again, just nothing 
> happens when I double-click on it. I can neither partition it, nor 
> change it to ext4 and mount it.
> 
> So it looks like there's work remaining to make this usable in CentOS too.

Maybe, but your setup is pretty unusual. These MD arrays are "disks" for
the installer, and thus would need to be partitioned. I believe it would
work better that way. I have never tried an LVM PV on a whole disk.

Martin

> 
> Regards,
> 
> Brian.
>