VM NIC Won't Stay Connected

If you are having problems with a NIC staying connected, it could be due to the number of ports configured on the vSwitch. By default there are 24 ports configured, so if the number of virtual machines running exceeds that number they may start to become disconnected. Check /var/log/vmkernel for these messages:

Net: 1317: can't connect device: VM Network: Out of resources

If this is the case, then either move some VMs to a different vSwitch or increase the number of ports on the vSwitch. Increasing the ports will require a reboot.

Instance GUID is improperly specified

Recently I was trying to install vCenter when I received the error "Instance GUID is improperly specified". This was a brand new Windows 2008 Server and a fresh install of vCenter, but the problem was that the install had failed a few times already due to other issues and rolled back. It seems that the rollback process does not completely clean up the files it creates, because one such file called 'instance.cfg' is created in c:\Program Data\VMware\VMware VirtualCenter and in it there is a line with the GUID. So to resolve this, simply delete that file and it will be recreated upon installation.

ESX Host Loses Connectivity Briefly

I have seen this issue with ESX 3.5 Update 2 and Update 4, the host disconnects briefly from the console and there are no real error messages in VirtualCenter other than indicating the disconnection.

Some research revealed that this is due to a memory leak in hostd. To mitigate the issue, I increased the Service Console memory 800 MB and the modified the soft and hard memory limits in the config.xml file.

You can identify this issue from the following errors in /var/log/vmware/hostd.log:

[2009-09-29 01:25:54.857 'Memory checker' 19467184 warning] Current value 204800 exceeds soft limit 122880.
[2009-09-29 01:26:24.868 'Memory checker' 18668464 warning] Current value 204800 exceeds soft limit 122880.
[2009-09-29 01:26:54.879 'Memory checker' 3076465568 error] Current value 204852 exceeds hard limit 204800. Shutting down process.

To change the console memory configuration from the default of 272 MB with ESX 3.5 to the max of 800 MB, edit the memory settings from VirtualCenter under Configuration -> Memory -> Properties. This change requires a server reboot.

To change the hard/soft limits, add the following into the <config> section of /etc/vmware/hostd/config.xml
<hostdWarnMemInMB>300</hostdWarnMemInMB>
<hostdStopMemInMB>380</hostdStopMemInMB>

Do a restart on hostd process by:
service mgmt-vmware restart

Unable to Apply DRS Resource Settings on Host

"Unable to apply DRS resource settings on host (Reason: A general system error occurred: Invalid fault). This can significantly reduce the effectiveness of DRS"

Check each VM running on the host to make sure VMTools is unmounted. I had one machine with the tools still mounted, as soon as I ended the tools install, the error resolved on its own and the host was fully integrated into the cluster.

Error 25003. Setup failed to create the vCenter Server repository

http://www.vmware.com/support/vsphere4/doc/vsp_esxi40_vc40_rel_notes.html

vCenter Server installation on Windows Server 2008 with a remote SQL Server database fails in some circumstances
If you install vCenter Server on Windows 2008, using a remote SQL Server database with Windows authentication for SQL Server, and a domain user for the DSN that is different from the vCenter Server system login, the installation does not proceed and the installer displays the following error message:
25003.Setup failed to create the vCenter repository.
Workaround: In these circumstances, use the same login credentials for vCenter Server and for the SQL Server DSN.

Storage vMotion Enhancements

Improved scalability

Improved performance

Less resource utilization

UI support

Migrate between thick and thin disks

Convert RDMs to VMDKs

No memory doubling requirement

Move a VM's storage from VMFS to NFS

Change storage while VM is running

Quick Hit - New vSphere 4 Storage Features

Paravirtualized iSCSI

What: This is a driver for high performance storage adapters

Benefits: It offers greater throughput and lower CPU utilization

When to use it: For very I/O intensive applications

VMDirect I/O for Storage

What: Enables VMs to directly access the underlying hardware

Benefits: Enhances CPU efficiency in applications with constant and frequent I/O

Drawbacks:
     1) VMotion is not available
     2) HBA is not shareable by other VMs

Virtual Disk Thin Provisioning

What: Space is allocated on an as-needed basis in 1 MB chunks

Benefits:
     1) Improves storage efficiency
     2) Increases utilization rates
     3) Reduces storage costs

Drawbacks: You could over provision the disks and run out of space, so monitoring of resources is essential.