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Setting up Fakeraid with mdadm

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  Setting up Fakeraid with mdadm "Christoph Pleger" <Christoph.Pleger@cs.tu-dortmund.de> - 2016-03-24 12:10 +0100
    Re: Setting up Fakeraid with mdadm Dan Ritter <dsr@randomstring.org> - 2016-03-24 13:00 +0100
      Re: Setting up Fakeraid with mdadm "Christoph Pleger" <Christoph.Pleger@cs.tu-dortmund.de> - 2016-03-24 14:00 +0100
        Re: Setting up Fakeraid with mdadm "Christoph Pleger" <Christoph.Pleger@cs.tu-dortmund.de> - 2016-03-24 15:10 +0100
        Re: Setting up Fakeraid with mdadm Dan Ritter <dsr@randomstring.org> - 2016-03-24 16:10 +0100
          Re: Setting up Fakeraid with mdadm "Christoph Pleger" <Christoph.Pleger@cs.tu-dortmund.de> - 2016-03-24 17:10 +0100
            Re: Setting up Fakeraid with mdadm Dan Ritter <dsr@randomstring.org> - 2016-03-24 17:30 +0100

#165902 — Setting up Fakeraid with mdadm

Hello,

I am trying to use an "LSI Megaraid Software RAID" with mdadm, but I have
not been successful so far. When I configure a RAID 1 in the BIOS
Setup-Utility and boot from network with an NFSROOT, a ddf container
device is detected as /dev/md127 and a raid device as /dev/md126, but when
I reboot, the previously created RAID configuration has been destroyed,
that is, when I start the BIOS-RAID-Utility again, it does not 'remember'
the configuration it created earlier.

As a solution of the above problem, I already tried to create an mdadm
RAID 1 without BIOS support, that is, I deactivated the RAID feature in
BIOS-Setup and after booting with NFSROOT, used 'mdadm --create ...', but
I did not manage to make that RAID bootable.

So, how can I setup a RAID 1 over two whole disks with mdadm?

Regards
  Christoph

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#165905

On Thu, Mar 24, 2016 at 11:52:05AM +0100, Christoph Pleger wrote:
> Hello,
> 
> I am trying to use an "LSI Megaraid Software RAID" with mdadm, but I have
> not been successful so far. When I configure a RAID 1 in the BIOS
> Setup-Utility and boot from network with an NFSROOT, a ddf container
> device is detected as /dev/md127 and a raid device as /dev/md126, but when
> I reboot, the previously created RAID configuration has been destroyed,
> that is, when I start the BIOS-RAID-Utility again, it does not 'remember'
> the configuration it created earlier.
> 
> As a solution of the above problem, I already tried to create an mdadm
> RAID 1 without BIOS support, that is, I deactivated the RAID feature in
> BIOS-Setup and after booting with NFSROOT, used 'mdadm --create ...', but
> I did not manage to make that RAID bootable.
> 
> So, how can I setup a RAID 1 over two whole disks with mdadm?

You can either use the LSI's built-in RAID system or mdadm but
not both. Don't use the fakeraid. If you actually have a decent
LSI card (2002 or 3003 chipset) you could use the real RAID that
is provided there, instead. In that case, RAID will show up as
/dev/sda.

Configure the LSI to present individual disks and then use mdadm
the normal way: partition the disks into two sets, a small /boot
partition and a large /. (Or three partitions per disk: /boot, /
and /home.)

Create mdadm pairs for each of sda1,sdb1  sda2,sdb2  sda3,sdb3
... and set /dev/md0, for /boot, as bootable. The Debian
installer can handle all of this easily.

-dsr-

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#165907

Hello,

> Configure the LSI to present individual disks and then use mdadm
> the normal way: partition the disks into two sets, a small /boot
> partition and a large /. (Or three partitions per disk: /boot, /
> and /home.)
>
> Create mdadm pairs for each of sda1,sdb1  sda2,sdb2  sda3,sdb3
> ... and set /dev/md0, for /boot, as bootable. The Debian
> installer can handle all of this easily.

Isn't it possible to use mdadm for mirroring disks as a whole, instead of
single partitions?

I am not using the debian installer, but want to boot from network with an
NFSROOT, create a basic system on the RAID and then reboot from RAID.

Regards
  Christoph

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#165909

Hello,

> Isn't it possible to use mdadm for mirroring disks as a whole, instead of
> single partitions?

If mdadm cannot create such RAIDs, is it possible to disable mdadm and use
dmraid instead? On the web, I have found information about a kernel
command line option 'nomdmonddf', but almost all of the information had to
do with Ubuntu, so I do not know if 'nomdmonddf' also works for Debian.

Regards
  Christoph

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#165911

On Thu, Mar 24, 2016 at 01:52:30PM +0100, Christoph Pleger wrote:
> Hello,
> 
> > Configure the LSI to present individual disks and then use mdadm
> > the normal way: partition the disks into two sets, a small /boot
> > partition and a large /. (Or three partitions per disk: /boot, /
> > and /home.)
> >
> > Create mdadm pairs for each of sda1,sdb1  sda2,sdb2  sda3,sdb3
> > ... and set /dev/md0, for /boot, as bootable. The Debian
> > installer can handle all of this easily.
> 
> Isn't it possible to use mdadm for mirroring disks as a whole, instead of
> single partitions?

Yes, but if it's going to be your main boot and root, don't do
that.

> I am not using the debian installer, but want to boot from network with an
> NFSROOT, create a basic system on the RAID and then reboot from RAID.

That's fine. All of this can be done by hand with fdisk or
parted, mdadm, and mkfs.

-dsr-

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#165916

Hello,

>>
>> Isn't it possible to use mdadm for mirroring disks as a whole, instead
>> of
>> single partitions?
>
> Yes, but if it's going to be your main boot and root, don't do
> that.

How is that done if it is not the boot disc? And why can it not be the
boot disc, though it could with dmraid?

I am still wondering why mdadm discovered the RAID that I had created with
the BIOS RAID utility, but destroyed it. I wanted to re-install the
machine anyway, but what if had used netboot with nfsroot as a rescue
system for the machine?

Regards
  Christoph

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#165918

On Thu, Mar 24, 2016 at 05:08:06PM +0100, Christoph Pleger wrote:
> Hello,
> 
> >>
> >> Isn't it possible to use mdadm for mirroring disks as a whole, instead
> >> of
> >> single partitions?
> >
> > Yes, but if it's going to be your main boot and root, don't do
> > that.
> 
> How is that done if it is not the boot disc? And why can it not be the
> boot disc, though it could with dmraid?


If it's not the boot disk, you do:

# mdadm --create --level raid1 -n 2 /dev/sda /dev/sdb

or other options that make you happy.

If you do this, you can make a filesystem in your new md device,
or you can try to partition it and then make filesystems. This
approach, in my experience, leads to confused initramfs and grub
configs that take hours to debug. So my advice is: don't do
that.

-dsr-

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