Re: [gentoo-user] raid1 + lvm2

[Jim Burwell]

Jarry wrote:

>Hi,
>
>I'm going to re-install gentoo on a small hobby-server and because
>I need both redundancy and flexibility, I thought in addition to
>raid1 (2x 160GB ata-disk) this time I would also use lvm2:
>
>/dev/md0 /boot   (~50MB)
>/dev/md1 /       (2GB)
>/dev/md2 <swap>  (2GB)
>/dev/md3 lvm2    (rest for /var /tmp /usr /opt /chroot /home)
>
>Is this generaly advisable solution (lvm2 over raid1), or is there
>some risk in using raid1 together with lvm2 ?
>
>One more question concerning partition type:
>If I want to use raid1, I have to set all those 2x4 (hda+hdc) primary
>partitions as type fd (raid autodetect). Is it not problem later for
>lvm2 when preparing and creating volume-group? Because lvm-guide says
>something about setting partition type to 8e (linux lvm), which I can
>not do, if I want to use raid1...
>
>Jarry
>
>

I recently set up a server like this.  I have /boot, swap, and root 
mirrored using linux RAID (md), and swap and root partition is an LVM2 
partition.

There's no problem with setting the partition types of 0xfd.  LVM2 
doesn't have a problem with it.

One thing you need is a initrd or initramfs setup to get all this stuff 
up and running during boot.  I found the easiest way to do this was to 
use genkernel.  Here's are some quick notes on how I got this working 
using the gentoo-sources-2.6.14-r2 kernel:

    Create your partitions using fdisk (/boot, and LVM2 partition for
    swap and root) on both disks.
    Set up RAID1 mirroring for these partitons (/boot md0, LVM2
    swap/root md2)

    Add the md1 device as a physical volume, and create a volume group
    and logical volumes for swap and root inside it.

    Do high level formats on your new /boot partition and root volume,
    and mkswap on your swap volume..

    Use genkernel to configure your kernel making sure to include this
    option: --lvm2

    Make sure the linux RAID (md) stuff is compiled into the kernel. 
    The LVM2 (dm) stuff can be modules.

    Make sure you include these kernel flags in your grub.conf or
    lilo.conf file:

         root=/dev/ram0 init=/linuxrc real_root=/dev/vg00/root dolvm2
        lvmraid=/dev/md0 lvmraid=/dev/md1

(Those last two flags don't seem to be documented anywhere, but are 
required for the genkernel produced linuxrc scripts in the initramfs to 
start up the md devices before it scans for the LVM2 stuff)

All this is probably easier done, if possible, during the install from a 
livecd.  I did it backwards myself.  I got a basic gentoo system running 
on one drive with normal partitions, then transformed it into the 
RAID/LVM system.  I did this by creating the Linux RAID partitons on the 
second drive with 'missing components' using mdadm (I use mdadm instead 
of the traditional raidtools).  This allows you to create your RAID1 
volumes with only one drive, the volumes coming up in degraded mode.  
You can then do your LVM2 volume creation stuff and create your 
filesystems, etc, get them mounted, and copy your basic system from the 
non RAID drive to your new volumes.  Then you can update your fstab, set 
up your bootloader on the RAID drive, and test boot, etc, making sure 
the system comes up using the RAID/LVM2 setup, while having the original 
drive for backup in case things don't work.  Once you're confident 
things will come up on the RAID/LVM2 setup, you can repartition the 
original drive, and "hotadd" the partitions to your RAID volumes.  Linux 
RAID will then sync the formerly missing components, and voila, you now 
have a synced/clean RAID1 system.

Hopefully that all made sense.  I banged my head against it for a while 
getting this set up to boot up (the final key was the lvmraid= flags 
which cause the linxrc to start up the md devices.  I had to read 
through the linuxrc scripts to figure this one out).

Good luck.

-- 
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