Yes, another R12 post. It's all I've been doing lately.
When I first installed 11.5.3, I just went with the default two-tier architecture; Web & Forms on the middle-tier and Reports & CCM on the db host. After a while, I realized that was a mistake for my environment. I should have put everything but the db on the middle-tier. Live and learn, I guess.
R12 was my chance to partially correct that mistake. I had a grand plan to migrate my middle-tier services to a hot x86_64 box and leave my db on Solaris. I figured that would give me an easier path if I needed to scale out either tier.
Except Oracle doesn't have a supported upgrade path on multiple platforms yet.
So I bounced a couple ideas off a very helpful Oracle Support Tech and he prefaced each one with "This isn't supported, but you might try...". I finally settled on a plan and executed it.
First, I collapsed my 11.5.9 tiers on to a single Solaris box. I used the Metalink whitepaper and rapidclone to get everything on my db box.
Then, I upgraded to 12.0.0 and applied the 12.0.4 RUP. At that point, I had a working 12.0.4 system with all my middle tier services on Solaris.
Next, I did a fresh install of 12.0.0 on a Linux box telling the configuration that I was going to have two tiers and my db was going to be on Solaris. Then I deleted my network topology and reran autoconfig that populated the db piece of my topology.
The next step was to apply the 12.0.4 patch to the Linux box. I did this with adpatch, but used the "nodatabaseportion" option because I knew I had already applied the object changes to my db.
The final step was running autoconfig on the middle-tier.
Except for a few glitches here and there, it was a surprisingly straight-forward split. Either I'm starting to get this Oracle Apps stuff or Oracle is finally getting serious about their configuration management.