Meu RAID1 via rede DRBD deu kernel panic e matou minhas duas máquinas(ARGHHH!!!). Depois de vasculhar a net, achei no FAQ do OCFS2(primeiro lugar que eu devia ter olhado) o problema:

Q05 I encounter "Kernel panic - not syncing: ocfs2 is very sorry to be fencing this system by panicing" whenever I run a heavy io load? A05 We have encountered a bug with the default "cfq" io scheduler which causes a process doing heavy io to temporarily starve out other processes. While this is not fatal for most environments, it is for OCFS2 as we expect the hb thread to be r/w to the hb area atleast once every 12 secs (default). Bug with the fix has been filed with Red Hat and Novell. For more, refer to the tracker bug filed on bugzilla: http://oss.oracle.com/bugzilla/show_bug.cgi?id=671

Till this issue is resolved, one is advised to use the "deadline" io scheduler. To use deadline, add "elevator=deadline" to the kernel command line as follows:

1. For SLES9, edit the command line in /boot/grub/menu.lst. title Linux 2.6.5-7.244-bigsmp elevator=deadline kernel (hd0,4)/boot/vmlinuz-2.6.5-7.244-bigsmp root=/dev/sda5 vga=0x314 selinux=0 splash=silent resume=/dev/sda3 elevator=deadline showopts console=tty0 console=ttyS0,115200 noexec=off initrd (hd0,4)/boot/initrd-2.6.5-7.244-bigsmp

2. For RHEL4, edit the command line in /boot/grub/grub.conf: title Red Hat Enterprise Linux AS (2.6.9-22.EL) root (hd0,0) kernel /vmlinuz-2.6.9-22.EL ro root=LABEL=/ console=ttyS0,115200 console=tty0 elevator=deadline noexec=off initrd /initrd-2.6.9-22.EL.img

To see the current kernel command line, do:

cat /proc/cmdline

Fiz também a documentação de como foi feito isso, disponível no meu site. Configurando DRBD com OCFS2 Em Modo Ativo-Ativo