F16 - Converting to RAID1
 

OK, I'm a long-time RedHat/Fedora user, but some of the recent changes
(grub2, systemd, hal, etc.) are modifying or deprecating my tried and
true methods. The latest issue I've got is that I want to add a second
drive in a RAID1 config for my main data partitions. This is something
I had planned all along and thought it wouldn't be a big deal. I've
done it countless times before. I've even got much of the work already
done. There are just a few pieces that have changed and I want to make
sure I get it right the first time.

I recently built a new "main" machine for my home office. It plays many
roles including that of main Fedora workstation as well as main Fedora
server. I primarily use this machine to provide server functions but
do use it for things like photo/movie/mp3 processing, Amarok, GIMP,
etc. I built it right before Christmas with an SSD for everything
except for {swap}, /var, and /data, which is on a separate 2TB drive.
When originally built it only used one data drive because HDD prices
were high. A few weeks later I picked up a matching drive on special.
It's installed, has partitioned, RAIDed (degraded), formatted, and it
contains a copy of the data. The problem is I'm not 100% sure what I
need to do to get this thing converted over for the reboot.

The drives are /dev/sda (SSD), /dev/sdb (existing data drive with ext4
partitions), /dev/sdc (new data drive). Here's what I was planning to do:
1. Umount the two RAID devices with a current copy of data.
2. Edit /etc/fstab replacing Device IDs with new RAID devices
(UUID=???? becomes /dev/md?)
3. Make backup of /boot/grub2/grub.cfg
4. Make backup of /boot/initramfs-$(uname -r).x86_64.img
5. dracut --force initramfs-$(uname -r).img $(uname -r)
6. grub2-mkconfig -o /boot/grub2/grub.cfg
7. I don't think I need to install grub2 on the new drive because
that's already on the SSD primary drive.
8. Do I need to remove the "rd.md=0" from /etc/default/grub? Or will
grub-2-mkconfig fix this?
9. Reboot and hope it starts with the new RAID devices (did I mention
that /var is on this disk as well?)
10. Modify partition types of /dev/sdb to fd (linux raid autodetect)
11. Add /dev/sdb to the RAID1 arrays and let them sync (mdadm --add
/dev/md? /dev/sdc?)


I would appreciate any advice.


Thanks,
-Brian
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F16 - Converting to RAID1
 

Brian Hanks writes:


1. Umount the two RAID devices with a current copy of data.
2. Edit /etc/fstab replacing Device IDs with new RAID devices
(UUID=???? becomes /dev/md?)


Although you can, /etc/fstab should still refer to filesystem UUIDs. If
you're switch partitions, /etc/fstab will simply need to refer to the
correct filesystem, by its uuid. As long as the md arrays get assembled
properly, and contain a usable filesystem, select the filesystem by UUID.



3. Make backup of /boot/grub2/grub.cfg
4. Make backup of /boot/initramfs-$(uname -r).x86_64.img
5. dracut --force initramfs-$(uname -r).img $(uname -r)


My favorite trick is run plymouth-set-default-theme with the --rebuild-
initrd flag, that causes the current kernel's initramfs to get rebuilt.
Right now, plymouth has a bug where it adds a redundant grub menu entry each
time you run it, which will need to be manually dropped, and in your case it
wouldn't matter because you're about to run grub2-mkconfig anyway.



6. grub2-mkconfig -o /boot/grub2/grub.cfg
7. I don't think I need to install grub2 on the new drive because
that's already on the SSD primary drive.


Correct. grub2 only needs to be installed on the boot drive.


8. Do I need to remove the "rd.md=0" from /etc/default/grub? Or will
grub-2-mkconfig fix this?


No, grub2-mkconfig won't fix it, and you will need to do it yourself.

Additionally, it's necessary to add the boot parameters

rd.md.uuid={uuid}

to the kernel boot line, for every mdraid device, where {uuid} is the MD
uuid, not the filesystem uuid. That's the uuid reported by mdadm --detail
/dev/mdN


Although it's been my experience that mdraid volumes usually still get
assembled at system boot time even in the absence of an explicit rd.md.uuid
boot parameter, the problem is the "usually" part, and I've had persistent
problems with one of the RAID-1 volumes inexpicably coming up degraded,
after a reboot, with one of the devices missing, forcing me to add it
manually, and then wait for the array to resync.


This got old very quickly, and I just didn't want to waste time any more
figuring out what's broken in initscripts, plus, without an explicit
declaration the undeclared RAID volumes were getting assigned a high minor
device number, like /dev/md127, rather than an expected low number. Which
was a little bit of an eyesore, but after I figured out that my problem was
the missing boot parameter, and added an explicit boot parameter for the
partition, the problem went away, and the array was assigned a reasonable,
low /dev/md minor device number.


The end result is that the boot parameters will get the arrays built at the
system boot, by their MD uuids first, then mount can find their filesystem
uuids, and mount them.


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F16 - Converting to RAID1
 

On 01/02/2012 03:31 AM, Sam Varshavchik wrote:

> without an explicit declaration the undeclared RAID volumes were getting assigned a high minor device number, like /dev/md127, rather than an expected low number. Which was a little bit of an eyesore, but after I figured out that my problem was the missing boot parameter, and added an explicit boot parameter for the partition, the problem went away, and the array was assigned a reasonable, low /dev/md minor device number.

It is not necessary to declare volumes with boot parameters.
I've found that having a proper line in mdadm.conf is enough; but you have to
rebuild the initramfs, because it contains a copy of the mdadm.conf.

A file like:

MAILADDR root
AUTO +imsm +1.x -all
ARRAY /dev/md0 UUID=xxxxxxxx:xxxxxxxx:xxxxxxxx:xxxxxxxx

(with correct UUID)
will be enough to avoid /dev/md127.

--
Roberto Ragusa mail at robertoragusa.it
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F16 - Converting to RAID1
 

Many thanks for the suggestions and validation. I modified my process
steps per the suggestions and I just executed all of the steps. It
worked flawlessly.


Thanks again,
-Brian
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