You can disable the default sparse LUN support to decrease the time ESX/ESXi needs to scan for LUNs.

The VMkernel provides sparse LUN support by default. The sparse LUN support enables the VMkernel to perform uninterrupted LUN scanning when a storage system presents LUNs with nonsequential LUN numbering, for example 0, 6, and 23. If all LUNs that your storage system presents are sequential, you can disable the sparse LUN support.


In the vSphere Client inventory panel, select the host, click the Configuration tab, and click Advanced Settings.


In the Advanced Settings dialog box, select Disk.


Scroll down to Disk.SupportSparseLUN, change the value to 0, and click OK.