A few tidbits re ZFS Root

I was lurking in #opensolaris @ irc.freenode.net when drdoug007 mentioned he'd been blogging about an intense Solaris minimisation project. I had a look... he's managed to get the entire image to around 42Mb uncompressed.

I then noticed he had a few entries re ZFS Root, and I remembered that there were three things I've discovered over the past week courtesy of my adventures with the ZFS delete queue that I really should mention.

(1) When you boot single-user off media, you need to ensure that your boot archive contains a version of the zfs module which has the same on-disk filesystem format. In the process of repeated bfus and update_nonONs I'd also upgraded my ondisk format from ZFS Version 1 to ZFS Version 3. The older module doesn't like the newer format. I yelled a bit when I realised this (it was a Friday evening.....).

Lesson: always make sure that your media is up to date with your on-disk format!

(2) The next thing I realised was that if you zfs export your root pool before you reboot (so that you can boot from the allegedly-fixed ondisk boot archive) then you'll see a panic on the next boot because your pool isn't imported and therefore the boot archive won't know where to look for the rest of the OS. That's a bit of an annoyance, to say the least!

Lesson: DON'T EXPORT YOUR ROOT POOL!!!

(3) I had to boot off media a few times because I stuffed up my boot archive. I found that in that scenario there was a gap in the bootadm logic which meant that effectively zero-length archives were created since lofiadm and zfs wouldn't play nice with each other.

Lesson: when booting to single-user, mount -o remount,rw / ;  cp {root_pool/root_filesystem}/usr/bin/mkisofs /usr/bin




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I work at Oracle in the Solaris group. The opinions expressed here are entirely my own, and neither Oracle nor any other party necessarily agrees with them.

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