Recovering Ubuntu 12.04 ZFS on Linux root pool mirror boot failure 3

Recently I ran into a problem booting my root ZFS mirror. Couldn’t get it to load, and only saw blinking cursor or blank screens. Grub could see the FS though!  I suspect I had a corrupted or out-of-sync zpool.cache file. Don’t ask me how that can happen, because the whole reason I run ZFS is so things like this don’t happen, yet on Linux the zpool.cache can be messed up somehow!  What I *think* had happened, is having something to do with all the recent zpool changes I had made recently. I had a couple pools of drives that I moved out of this system and kept only the root pool mirror for my development system.  So I don’t have answers for why the cache gets messed up, I do think my changes recently had something to do with it.  Probably something I did!

So I booted to thumb drive that had 12.04 server installed. I suppose you could just as easily use a LIVE DVD or USB stick, but you’ll need to apt-get install the zfs packages.

After I booted my thumb server, I updated zfs-linux packages!! Couldn’t get to the drives until it was updated because of the new ZFS format. I think the pool format version was 5000 and the older ZFS utils didn’t work with it. Having installed a handful of FreeBSD and Ubuntu servers with ZFS now, I am thinking better to create root ZFS pools using version=28 for better compatibility. I think that’s the advice of the ZFS On Linux people too.

Anyway, once server had working ZFS, I exported everything, and reimported like below:

zpool export rpool

zpool import -d /dev/disk/by-id -f -N rpool

Now that I had my rpool imported but NOT mounted, I will mount it so I can replace the cache. (NOTE: I am using /mnt/rootfs as my mount point, but instructions online typically have you mounting to /root, just replace as you see best for your system)

mount -t zfs -o zfsutil rpool/ROOT/ubuntu-1 /mnt/rootfs

The guides online tell me, DO NOT MOUNT other file systems! (ok, got it!) Just copy over the zpool.cache. I made a backup first, just in case.

cp /etc/zfs/zpool.cache /mnt/rootfs/etc/zfs/zpool.cache


Did a chroot into my mirror, updated /etc/default/grub
to show text only boot console.
Did an update-initramfs -c -k all
Ran grub-install /dev/sda and /dev/sdc (which are my mirror drives)
And lastly, update-grub.

Exit chroot environment.
Unchroot and unmounted /mnt/rootfs.
Reboot! Success!