Our project are plan to migrate from Sparc to x86, and our HA requirement is 99.99%, previous on Sparc, we assume the hardware stability would like, hardware failure every 4 month or even one year, and also we have test data for our application, then we have requirement for each unplanned recovery (fail over) to achieve 99.99% (52.6 minutes unplanned downtime per year).

But since we are going to use Intel x86, it seems the hardware stability is not so good as Sparc, but we don't have the detail data.

So compare with Sparc, how about the stability of the Intel x86, should we assume we have more unplanned downtime? If so, how many, double?

Where I can find some more detail of this two type of hardware?