Dumping to swap hangs

[Seeker]

Swap is on bsdlabeled third slice and /var/crash is in ZFS pool which consumes whole 4th slice
Whenever kernel panic occurs and dumping starts, it hangs at start:

... kernel: Dumping 316 MB:

What could be a cause?!
I had geli encrypted swap with permanent key and I also tried without geli swap at all and it is always same.

 

[Seeker]

When panic occurs there is no dump, BUT, when I issue:

# reboot -d

Dump occurs and I can get in /var/crash

Problem is it dump soooo slow, like 5 sec for 16 MB and not at all when panic occurs?

I use 8.2 RC-2