CentOS - Jan 2017 - CentOS 7 install on one RAID 1 [not-so-SOLVED]

So, it installed happily.

Then wouldn't boot. No problem, I'll bring it up with pxe, then chroot
and
grub2-install.

Um, nope. I edited the device map from hd0 and hd1 being the RAID to
/dev/sda and /dev/sdb, then ran grup2-install. It now tells me can't
identify the filesystem on hd0, and can't perform a safety check, and
gives up.

What am I missing? Google is not giving me any answers....

      mark

On Tue, January 24, 2017 4:14 pm, m.roth at 5-cent.us
wrote:
> So, it installed happily.
>
> Then wouldn't boot. No problem, I'll bring it up with pxe, then
chroot and
> grub2-install.
>
> Um, nope. I edited the device map from hd0 and hd1 being the RAID to
> /dev/sda and /dev/sdb, then ran grup2-install. It now tells me can't
> identify the filesystem on hd0, and can't perform a safety check, and
> gives up.
This is an interesting logical contradiction (unless things progressed
much farther than what I last read):

If you want to boot off your RAID1 device you need software RAID piece of
code already running, i.e. kernel already loaded, to load which which in
the first place you needed md0 or whichever device to exist to load it
from...

The only way around that I remember people were using was: cutting small
partition off the drive to keep it as a regular partition, and have /boot
on it. The rest of the drive can be different partition which can
participate in software RAID. For mirror (RAID-1) I remember people were
cutting the same piece off the beginning of both drives, one is always
active /boot (another can be maintained as a copy of it, but if you loose
first drive, you will need to install grub bootsector to second drive
pointing to /boot copy on that drive for loading initramdrive).

Anyway, good luck. Getting hardware RAID controller will be waaay less
hassle at all stages of your machine's life.

Valeri
>
> What am I missing? Google is not giving me any answers....
>
>       mark
>
> _______________________________________________
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>

++++++++++++++++++++++++++++++++++++++++
Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
++++++++++++++++++++++++++++++++++++++++

On 01/24/2017 02:14 PM, m.roth at 5-cent.us wrote:
> So, it installed happily.
> Then wouldn't boot.

What did the storage configuration look like, exactly?  I'd guess that 
you put one partition on each disk, combined those in a RAID1 MD array, 
made than an LVM physical volume, and then created filesystems and swap 
on LVs.  But that's a lot of guesses.  Did you use MBR partitions or 
GPT?  Are you booting under BIOS or UEFI?  Where do your partitions 
start?  Did you create a standard MD RAID volume and LVM or a 
partitionable RAID volume and partitions?

On Tue, 2017-01-24 at 17:14 -0500, m.roth at 5-cent.us
wrote:
> So, it installed happily.
> 
> Then wouldn't boot. No problem, I'll bring it up with pxe, then
chroot and
> grub2-install.
> 
> Um, nope. I edited the device map from hd0 and hd1 being the RAID to
> /dev/sda and /dev/sdb, then ran grup2-install. It now tells me can't
> identify the filesystem on hd0, and can't perform a safety check, and
> gives up.
> 
> What am I missing? Google is not giving me any answers....
> 
Surely, if you are using software RAID, then you should configure that
RAID in anaconda, that will then cope with setting up the partitions to
allow booting.  Basically it needs a small non-RAID partition to hold
/boot on the boot disk.

Remember that the boot sequence is generally: BIOS reads MBR and
executes it; MBR code reads kernel from /boot and executes it (yes,
it's more complicated than that). If the MBR code doesn't know how to
read a RAID partition, then it's going to fail, that's why you have a
small non-RAID partition to hold /boot.

Hardware RAID is different because it interfaces at the BIOS level so
the MBR code doesn't need to know how to specifically read it.

P.

On 01/24/17 19:00, Gordon Messmer wrote:
> On 01/24/2017 02:14 PM, m.roth at 5-cent.us wrote:
>> So, it installed happily.
>> Then wouldn't boot.
>
> What did the storage configuration look like, exactly?  I'd guess that
you put
> one partition on each disk, combined those in a RAID1 MD array, made than
an
> LVM physical volume, and then created filesystems and swap on LVs.  But
that's
> a lot of guesses.  Did you use MBR partitions or GPT?  Are you booting
under
> BIOS or UEFI?  Where do your partitions start?  Did you create a standard
MD
> RAID volume and LVM or a partitionable RAID volume and partitions?
No. Brand new machine, pulled it out of the box and racked it. NOTHING on the 
internal SSDs. Made an md RAID 0 on the raw disks - /dev/sda /dev/sdb. No 
partitions, nothing. However, when I bring it up, fdisk shows an MBR with no 
partitions. I can, however, mount /dev/md127p3 as /mnt/sysimage, and all is
there.

Did I need to make a single partition, on each drive, and then make the RAID 1 
out of *those*? I don't think I need to have /boot not on a RAID.

	mark

In article <1485342377.3072.6.camel at biggs.org.uk>,
Pete Biggs <pete at biggs.org.uk> wrote:
> On Tue, 2017-01-24 at 17:14 -0500, m.roth at 5-cent.us wrote:
> > So, it installed happily.
> > 
> > Then wouldn't boot. No problem, I'll bring it up with pxe,
then chroot and
> > grub2-install.
> > 
> > Um, nope. I edited the device map from hd0 and hd1 being the RAID to
> > /dev/sda and /dev/sdb, then ran grup2-install. It now tells me
can't
> > identify the filesystem on hd0, and can't perform a safety check,
and
> > gives up.
> > 
> > What am I missing? Google is not giving me any answers....
> > 
> 
> Surely, if you are using software RAID, then you should configure that
> RAID in anaconda, that will then cope with setting up the partitions to
> allow booting.  Basically it needs a small non-RAID partition to hold
> /boot on the boot disk.
> 
> Remember that the boot sequence is generally: BIOS reads MBR and
> executes it; MBR code reads kernel from /boot and executes it (yes,
> it's more complicated than that). If the MBR code doesn't know how
to
> read a RAID partition, then it's going to fail, that's why you have
a
> small non-RAID partition to hold /boot.
> 
> Hardware RAID is different because it interfaces at the BIOS level so
> the MBR code doesn't need to know how to specifically read it.
If you are using RAID 1 kernel mirroring, you can do that with /boot too,
and Grub finds the kernel just fine. I've done it many times:

1. Primary partition 1 type FD, size 200M. /dev/sda1 and /dev/sdb1.
2. Create /dev/md0 as RAID 1 from /dev/sda1 and /dev/sdb1.
3. Assign /dev/md0 to /boot, ext3 format (presumably ext4 would work too?)
4. Make sure to setup both drives separately in grub.

Typically I then go on to have /dev/sda2+/dev/sdb2 => /dev/md1 => swap,
and /dev/sda3+/dev/sdb3 => /dev/md2 => /

Cheers
Tony
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org