support crash dumps to raidz, etc. pools
Most systems are configured with a dedicated system pool: a pool which contains the installed OS, swap device, dump device, configuration, and other artifacts. It's standard for the system pool to be configured with a mirrored pair of disks, so the crash dump support on ZFS only supports dumping to a single disk or a mirrored vdev.
However, we (Joyent) are using a different model. Our systems PXE boot from a central server and run the OS image straight from memory rather than installing it to any disks. We configure one pool which contains the typical "system" data as well as customer data. Since this pool can't be a single mirrored vdev, we've enhanced the crash dump code to support dumping to all types of pools: raidz, raidz2, raidz3, pools with multiple vdevs, and pool which may contain log, cache, and spare devices.