I have seen similar symptoms. In the end, I narrowed my problems down to a very particular combination of hard drive and laptop.
The installation would complete fine, but I would get i/o errors running plan9 from the (pata) hard disk. I tried with and without dma and rwm. "dd" read and write tests run from the installation disk all proved to be ok. Stand-alone hard disk and memory diagnostics didn't show up any hardware errors. Another hard drive worked fine with the same laptop and, bizzarely, the hard drive worked fine with plan9 in a different laptop. Debian and windows installed and ran fine. Interestingly, I had another laptop of the same model (inspiron 3500) which also failed identically. I concluded that there was most likely something about the timing in the ata driver that tickled the drive/interface combination. Rod
