Thanks for the reply. This is truly weird. I think it just takes awhile for the system to 'warm up' or cache the content on the partition ? I am not sure what happened, but I just went back and test it again, the speed comes back normal. Maybe it has something to do with the size of the partition? Each partition is 1TB in size. But to answer your question:

When you create and mount each device exclusively, are the speeds still the same?

Yes, speed is the same when I mount one or both partitions. Actually the number I listed was from mounting one partition at a time. I have no previous experience with RAID, my guess is that it probably has something to do with some library. I can read files but it's super slow. VLC said something about buffering when I tried to play a media file on the partition.

The two disks are both 2TB Hitachi server drives, usually I can hear some noise in Windows when I read/write the partition but they are very quiet in Ubuntu when I read, not sure what's happening here. Nothing outstanding is showing up in the SMART info either.

And how are you benchmarking?

I got the the speed from rsync with --progress flag. I am not very concerned about the number listed but the actual speed. I cannot watch videos on the RAID0 partition, and I know there's is definitely something off when ls -lah takes more than a second to show my 20 something files in the root of the partition.

And there was nothing unusual in the logs about the devices?

Hmm, what log do you suggest I check? dmesg doesn't show nothing abnormal. I get no error message when I mount the partition.

Ah well, I guess the problem solved itself.