3rd hang of Nexenta in a row

I did a fresh install of NexentaStor, configured RAID-Z of 4 2TB drives and managed to copy almost all my archive of 1.5 TB over NFS. Now Nexenta hangs again.
Nexenta was about twice as fast as FreeNAS with same ZFS configuraiton. I was writing at 54 MB/s sustained.

Interesting.
root@nexenta:/# ls -l core
-rw------- 1 root root 3089329786 Dec 3 20:45 core
root@nexenta:/# file core
core: ELF 64-bit LSB core file AMD x86-64, version 1 (SYSV), SVR4-style, from '8*'

A few such cores, and root will be full.

root@nexenta:/# strings core |less
X"'7
CORE
zdb -D tank
CORE
i86pc

I guess this is a core from zdb, which man page says not to run unless asked by support. Nexenta runs it for reporting, apparently.

root 3900 766 0 22:00:34 ? 0:02 /usr/bin/perl /var/lib/nza/triggers/volume-check
root 4596 3900 0 22:13:31 ? 0:23 zdb -D tank

Let's disable this coring for now

root@nexenta:/# coreadm
global core file pattern:
global core file content: default
init core file pattern: core
init core file content: default
global core dumps: disabled
per-process core dumps: enabled
global setid core dumps: disabled
per-process setid core dumps: disabled
global core dump logging: disabled
root@nexenta:/# coreadm -d process