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Yesterday VMware released Update 4 for ESX 3.5 and ESXi 3.5. It includes a few new features but no major enhancements. It also has some limitations to go with it that are important to note.

Here are some of the highlights:

• ESX 3.5 U4 does not work with all versions of vCenter 2.5. For example, you will need to have vCenter updated to at least Update 3 in order to be able to use it to manage ESX 3.5 Update 4. There is a compatibility matrix of which versions of ESX work with specific versions of vCenter here (this link opens a PDF).
• You can now enable the Enhanced vmxnet driver for 32-bit operating systems. Previously you had to set the guest OS to a supported type (like Server 2003 x64), enable the Enhanced vmxnet NIC, and then change the OS back. This is no longer required. This driver enables advanced networking features like TCP Segmentation Offload.
• VMware has included experimental support for PXE booting ESXi hosts. This would allow you to have a completely stateless and diskless server with ESXi installed on a flash drive able to PXE boot and be ready to host virtual machines in minutes.
• A large number of new hardware devices are supported, including NICs, SATA controllers, etc.

The full release notes can be found here for ESX 3.5 and here for ESXi 3.5.

As with any update to ESX, make sure you do it in the proper order. First upgrade vCenter and your database and then update each of your hosts.

Ever since VMware announced that their ESXi hypervisor would be available free of charge, people have had a (somewhat) misguided notion that there is a “free version” of ESX.  I have heard phrases like, “Can I use the free version of ESX?” which then often leads to questions like, “If I need advanced features like VMotion, do I have to upgrade to the full version of ESX?”  These questions can lead to confusion so it is important to understand the basics of VMware’s free hypervisor.

In truth there is no free version of VMware ESX or ESXi, nor is there any need to upgrade from ESXi to ESX in order to use any of the advanced features of the product.

So then how can you run the ESXi hypervisor for free if there is no free version?  To better understand how this works, you should accept that there is no free version but rather a free license.   The free license, which is limited in features and functionality, can only be applied to the ESXi hypervisor and not the ESX hypervisor.  The actual version of ESXi is identical regardless of which license is used and only differs in the features that are available.

If additional features are desired, such as VMotion or High Availability, then the appropriate license must be purchased and applied to the ESXi installation (see chart below).  This can be done without reinstalling ESXi and all features available in VMware ESX are available in ESXi provided the right license is used.

VMware sells licenses for VI3 in three separate versions – Foundation, Standard, and Enterprise (see below for breakdown of which features are available in each version).  These licenses can be applied to an installation running either VMware ESX or ESXi, and a licensed copy of both ESX and ESXi will have the same features available.

VMware VI3 - How to Buy

That is not to say, however, that VMware ESX and ESXi are identical products.  They differ in their architecture in some important ways so there is value in understanding their differences.  VMware provides a nice KB article that describes these differences.

And finally, in truth nothing is ever really free and this is no exception.  In most circumstances you’ll want to purchase a support contract along with the free license of ESXi to make sure that you can call VMware to troubleshoot any issues that come up.