Had a customer report the above issue and have it fixed by IBM so I thought others might benefit from it. The issue has been fixed as IBM SPR# KBRN8AKKA9. The technote is 1449825 and contains a lot of good info. Setting notes.ini “Disable_Random_RW_File_ATTR=1” fixes the issue.
“After Domino opens many NSF files in quick succession during a backup, the Virtual Address Space of the OS system cache may be completely used up (for example, 1TB of data may be used in this OS cache). Successive calls into the OS cache manager to get memory from the OS system cache then results in mapping/unmapping of views from the system cache. These mapping/unmapping operations takes a lot of CPU time and as a result shows as high OS CPU usage. In addition, because the large OS system cache may now reside on the disk (the RAM is not large enough to hold the OS system cache) this results in significant I/O on the system.”