problems obtaining kernel dump

[Roman Bogorodskiy]

Hello,

I'm having a problem obtaining kernel dump. The box has 512Mb of RAM.

In rc.conf I have:

dumpdev="/dev/ad4s1b"
dumpdir="/var/crash"

swapinfo -h gives the following:

Device          1K-blocks     Used    Avail Capacity
/dev/ad4s1b       1048576       0B     1.0G     0%

/var/crash directory exists, and the root partition where it is placed
has enough space as well:

/dev/ad4s1a    989M    350M    560M    38%    /

The box runs fresh FreeBSD/i386 -CURRENT.

So, I do swapoff and then perform actions to reproduce the crash and it 
breaks me into ddb prompt.

I do:

call doadump
continue

it reboots, and when I run "savecore -v /var/crash /dev/ad4s1b" it
prints:

unable to open bounds file, using 0
checking for kernel dump on device /dev/ad4s1b
mediasize = 1073741824
sectorsize = 512
magic mismatch on last dump header on /dev/ad4s1b
savecore: no dumps found

The same happens when I do 'panic' instead of 'call doadump' like
handbook suggests. What am I doing wrong? I googled for similar
problems, found some mail threads but didn't find meaningful advises
though.

Roman Bogorodskiy