gptzfsboot very slow

[David Wimsey]

My file server is configured with zfs root based on http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/Mirror

When booting, after it gets past the BIOS drive C: is disk0 (one line for each of the 6 drives as expected) part, drops to a new line and the rotating twiddle starts its bit.  At first it moves a long at a almost normal looking speed, then it starts only ticking away slowly, maybe once or twice a minute.

It appears that its scanning the entire drive or something odd.  Its hard to tell if its doing it on all the drives as half of them are on a RocketRAID card (configured as JBOD) which doesn't have a LED indicator attached to it for showing activity.

There are a total of  6 drives in the machine.

2 drives are SSDs which are sliced up to provide the root mirror vdev, a mirrored vdev for the zip if the main pool on the machine and  each provide a slice L2ARC.  Some of the remaining space is in a small pool 
3 of the HDDs are part of a raidz vdev for my main pool.
The remaining HDD is a hot spare.

If I remove the HDDs from the system and just let the SSDs handle the boot, its faster but still far longer than it should be, so when I'm in a hurry I unplug the 4 HDDs, boot, wait for it to get to the FreeBSD boot menu, plug the HDDs back in and send it on its marry way.

This can not be expected behavior in my mind.  Why is it doing so much disk thrashing when the pools are all perfectly clean.