Sunday, July 01, 2012

Where computing takes you...

Do you ever have those afternoons you get a ”great” idea and you've all the evening time for that task. The task is a relaxing one and won't need much attention, and you can watch a movie or something.  But then, it happens that the evening turns into night as you realize a couple of little details adding complexity to the idea, and the task turns out to be much more invasive to your evening than you thought?

In this example, I got the great idea to upgrade my Debian running NAS device (thanks Martin for everything!) to use ext4 instead of ext3. The kind of idea that takes a long time for relatively little practical benefit, but it just feels like a nice thing do when you've the extra amounts of nerd time available. It's basically just opening the NAS device up, mounting its hard disk to a laptop via external case, running the tune2fs and fsck then putting the disk back. It just takes a long time for the initial fsck (to make sure everything's intact) and then the required fsck run to get ext4 mountable.

Only in this situation, it would have been beneficial to have the ext4 support in the flashed initramfs before the migration. So... before the photo below, I've already:
  1. done the ext4 migration and fsck:s
  2. screwed the disk back to the NAS case, attached cables and found that it doesn't boot
  3. (on the laptop with the hard disk attached again tried manually unpacking initramfs and adding ext4 module... also had time to bind mount everything and chroot into the ARM system to run update-initramfs manually... also tried booting with those... until remembered the simple fact that the /boot partition is only for show and also the initramfs is loaded directly from flash)
  4. copied the main root filesystem content from the original disk to another external disk with ext3 partition
  5. attached the another disk (with same UUID:s) to the QNAP NAS device, booted, double-checked that I have now ext4 specified under /etc/initramfs-tools/modules, reconfigured the linux image that also regenerates initramfs and flashes it
And in the photo, what's happening is that:
  1. I've again the original disk reattached and system booted with the initramfs generated and flashed from the ext3 disk
  2. the NAS device is hanging in the air, cover open, from the closet where I've things stuffed in (normally secured with cable ties), and I need to support it with a knee or one hand since the 2TB disk is much heavier than the small SSD I used as the ext3 disk so the power cable and RJ-45 cable would have pretty heavy load
  3. Since I've only one hand in use and can't use a laptop, I'm logging in via my Nokia N9 and then reflashing the kernel + initramfs from this original disk, just to make sure everything is now alright and also after that flashing it still boots (it does!). Note that I feel like the setup is secure enough for non-interrupted flashing so that I can indeed support the NAS with a knee, use one hand to keep N9 and another hand to take a photo with a camera.

And so we have had a productive and educating afternoon/evening/night once again. Does this ever happen to you?
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