Instant crash with ZFS + iozone?

[Lassi Tuura]

Hi,

I've just started playing with FreeBSD and ZFS.

I installed 8.0-RELEASE, then 8.0-STABLE 201004 (amd64) on a system with 4 * 1TB hard drives for ZFS (2 * Hitachi Deskstar 7K2000, 2 * Samsung SpinPoint F3), plus 2GB IDE flash for OS itself (Transcend), 4GB ECC RAM, AMD Athlon II X2 235e CPU, Asus M4A78L-M LE motherboard.

I can use the basic system fine. However when I create a ZFS volume out of the 4 disks and run iozone on it, the system will reliably die within 5 seconds or so, sometimes it takes a little longer, up to a minute or so.

By "die" I mean the screen goes completely blank, and it will no longer respond to anything - no network, not even ping and any existing network connections will die, no keyboard, screen totally black without as much as a cursor... nothing. The soft power button won't work either. AFAIK the only thing that works is the reset button.

When the system comes back, /var/log is silent on last 30 seconds preceding the crash. The same thing occurs with drives in ATA and SATA/AHCI mode in BIOS, with or without "ahci_load="YES"" in /boot/loader.conf.

So my first question as a FreeBSD newbie is: how do I get to see why this happens? It could be some simple hardware conflict, but how do I get the system to tell me what is wrong? Without even a panic message on screen I am a bit lost... If I get a serial-to-usb cable and send console there, would I see more? I don't currently configure a swap device; would that help to get a crash dump?

As far as I can tell, this is not caused by ZFS ARC. When I manage to run arcstats.pl and the system runs long enough, ARC size remains tolerable (~1GB) as long as I get output on screen. I did do the ZFS tuning guide's config in /boot/loader.conf, but it doesn't change anything. So far I am assuming some bad hardware interaction somewhere...

Regards,
Lassi