One possible root cause is that your computer uses Intel Smart Response Technology / Intel Rapid Storage Technology (ISRT / IRST), a kind of RAID. It is somehow unusual or different compared to older versions of RAID, and dmraid doesn't understand it. Looking around, I see a few approaches that people have taken..
(1) The approach I recommend is to install mdadm, which is (according to Intel) the modern replacement of dmraid. When mdadm is available -- even if dmraid is also installed -- the ubuntu installation will use mdadm to correctly understand what the partitions are. At least it worked for me. I posted details at another question.
(2) Another approach that many people have recommended is to turn off RAID altogether. This often involves changes in an Intel program that you run in Windows, and in BIOS. But the disc can still be left with RAID-type markings, and you have to run some commands to erase them before the disc is finally recognized as non-RAID (explanation of this part). For instructions in this method see here and here. Turning off ISRT / IRST would presumably reduce performance somewhat. On the other hand, it seems from those pages that it is possible to resurrect RAID (at least in windows) to improve the performance after installing ubuntu. But I don't know, it seems to me that this approach leaves ubuntu ignorant of RAID while windows is using it, so I doubt ubuntu will be able to access files created in windows. I could be wrong.
(3) Finally, the approach you mention is to delete dmraid. I'm not sure exactly what happens here. Clearly it has worked for many people, although one can find old reports from people who had a bit more hassle than just that. One could also find a long time later that dmraid has reinstalled itself (as the dependency of something else), and I don't know whether that could cause problems. The most obvious problem, as before, is that it seems dangerous if windows is using ISRT but ubuntu knows nothing about RAID, yet you want ubuntu to be able to access the files created by windows. I could be wrong...
