I just installed 8.1.7 on an Solrais 2.8 yesterday.
The only thing, which the doc is suck, is:

You need to run runInstaller in other directory other
than /cdrom/oracle8, and Oracle doc. says
run it under /cdrom/oracle8.

If you run runInstaller under /cdrom/oracle8, you will
not be able to switch to Disk2.

So, I did install twice!