The WP Engine Team worked endlessly to resolve the issues that plagued us since the issue was reported yesterday. The team made some final changes on our system and pushed those changes to the system. We believe the system is stable but if anyone sees any issues with their site, please let us know right away.
Here is what happened: The memory-mapped I/O for PHP Opcode was eating up the entire disk I/O. Due to the fact that this issue was buried in kernel virtual memory manager numbers and not in the usual disk I/O numbers, it took the team a long time to determine the issue and resolution. Several updates were made to the system, and this issue has been resolved.
As always, if you see any other issues, please contact the WP Engine Support Team!