This walkthrough is part II of a series of guides on installing and configuring VMware’s tools for updating and patching ESXi 4.1 hosts. You can find Part I here and Part III here. The Update Manager Download Service (UMDS) is used in an air-gap environment where the vCenter Update Manager server (VUM) does not have access to the Internet to download patches itself – instead it relies on UMDS to download the patches. Once patches are downloaded, they’re manually copied via removable media, usually a CD/DVD, to VUM. Once VUM has the patches, it then works through the vSphere Client and the Update Manager plug-in to update the hosts. Although VUM can download operating system patches for Windows and metadata for Linux patches, we’re not using this configuration in this guide. We’re assuming the environments are updated via WSUS or SCCM.