We currently have ESX 3.5 Update 2 installed on Dell PowerEdge 2900 & 1950 servers and we are using an EMC AX150i iSCSI SAN. Several months ago, we attempted to upgrade from Update 2 to Update 3 and it brought our entire infrastructure to it's knees. We were getting purple screens on all the hosts and VMs were randomly crashing. According to WMWare it was a known issue with 1 other major corporation but they didn't have a fix to provide. Thus, we have been waiting to upgrade as we don't want to run into a similar situation with Update 4.
Has anyone had any problems going to Update 4? More specifically, does anyone have a similar infrastructure as we do that is running ESX 3.5 Update 4?
We just completed our upgrade a few weeks ago of ~70 ESX Host to U4. Besides needing to update the guest tools, we haven't run into any issues.
However, our upgrades consisted of rebuilds, which is our preference.
I upgraded about 15 hosts from 3.5U3 to 3.5U4 with all patches up to and including the July 2009 patchset. At this point, we have no issues and we have been running on 3.5U4 for about 2 months. We have seen more stability and less storage related issues. For our process, I installed the 3.5U4 patch with no reboot and then installed all the following patches using a script (accounting for order since some patches have dependencies) and rebooted only once at the very end. Since I copied over the patches to /tmp/ first, you do need about 4.5 GB free on the / partition or not all the patches will install.