Harddisk Geometry problem

I've a problem with my new harddisks.
I get an geometry incorrect when I fire up fdisk from the sysinstall menu.
The geometry is: 121600/255/63
It is a mirrored array (Intel MatrixRAID RAID1) with two Seagate SV35.3 1000GB disks.

When I use it anyway it I found the following problems:
1K blocks total: 946015166 (very much less, but I think its normal)
1K blocks free(before putting anything on it): 870333954 (is this normal?)

But the real problem began when I used it to put data on it:
I was writing much data on it from to mv commands and was verifying some data with par2. Then all ssh shells wich where doing anything with the new disks freezed. After a while i decided (I couldn't kill one of them, it just keeped "running") to just reboot, and the shutdown failed (page fault I think).
When I finnaly booted it up again, I couldn't do fsck on this disk without give the -t ufs option. When I did give the -t ufs option all was clean. I just can mount it, but still I can't check it without the -t ufs option.

How can I fix it, or should I change the geometry and create the partition again? If so how can determine the geometry (I tried pfdisk on a bootable dos disk but it was showing a very low diskspace(something like 8GB or something)? What is wrong?
That doesn't cover my problem.
I found these messages but it doesn't cover the remaining problem: Hanging when write much at the same time.
could it be that your hard drive is dying? Check /var/log/messages for any interesting messages related to your hard drive. System musn't hang while doing a lot of I/O.
That would be very weird. I installed these drives today on my existing installation, they are brand new. But I could do a SMART test, but I think that's not the problem. Also /var/log/messages doesn't show any messages about the harddrives.

The system didn't hang, I could open new ssh connection and do anything. But when I did a cd to the directory the raid volume is mounted on that shell hangs too.