Recently when we were solving the USB/SD-card boot issue (link) we noticed that “Scan entity” tasks on some hosts took more than 15 minutes. In VMware Community there is a thread describing similar issue – https://communities.vmware.com/thread/470949. One post there mentioned that the problem only exists on hosts with FC storage.
Based on that information we did a test and results were following. Scan entity task took about 16 minutes on a host with 100+ FC LUNs. Scan entity task took about 1 minute on a same host with all FC LUNs disconnected (FC ports disabled). We also tested on host with about 10 LUNs – scan entity tasks took about 3 minutes. I have created a case to VMware to understand how is LUN count related with scanning for patches.