ZFS root File System

[Dan Nelson]

In the last episode (Feb 27), Matthew Dillon said:
> My experience with one of our people trying to do the same thing w/
> HAMMER...  we got it working, but it is not necessarily cleaner.
> 
> I'd rather just boot from a small UFS /boot partition on 'a' (256M or
> 512M), followed by swap on 'b', followed by the big-ass root partition on
> 'd' using your favorite filesystem.
> 
> The boot code already pretty much handles this state of affairs, one only
> needs:
> 
> (1) To partition it this way.
> 
> (2) Add line to /boot/loader.conf pointing the kernel at the actual root,
>     e.g. (in my case):
> 
> 	vfs.root.mountfrom="hammer:ad6s1d"
> 
> (3) Adjust sysctl kern.bootfile in e.g. /etc/sysctl.conf.  Since the
>     boot loader thinks the kernel is on / instead of /boot (because
>     /boot is the root from the point of view of the bootloader), it might
>     set this to "/kernel" instead of "/boot/kernel".  So you may have to
>     override it to make crash dumps and name lists work properly.
> 
> (4) Add a mount for the little /boot partition in /etc/fstab.

I find it better (and easier to recover if something bad happens) if you
create a /.boot filesystem with /boot and copies of
/{bin,sbin,lib,libexec,etc} from your root partition, then symlink /boot in
your root partition to /.boot/boot.  That way you have a minimal system with
recovery tools in case your non-UFS root has problems of any sort, and /boot
always points to what you (and makefiles) think it should.  If you have root
on mirrored disks, you can gmirror /.boot too.  Works great for ZFS; should
work for HAMMER.

-- 
	Dan Nelson
	dnelson at allantgroup.com