Recently I saw some clusters that are not patched and or where not aware that there were hotfixes.
So here is a list of required and optional Windows 2008R2 SP1 hotfixes.
This list is found on several pages on the web and could be handy.
Windows & Hyper-V : Required Hotfixes
Validate SCSI Device Vital Product Data (VPD) test fails after you install Windows Server 2008 R2 SP1
http://support.microsoft.com/kb/2531907 (required for 3+ node Hyper-V clusters)
The network connection of a running Hyper-V virtual machine may be lost under heavy outgoing network traffic on a computer that is running Windows Server 2008 R2 SP1
http://support.microsoft.com/kb/2263829
The Cluster service stops unexpectedly on a Windows Server 2008 R2 failover cluster node when you perform multiple backup operations in parallel on a cluster shared volume
http://support.microsoft.com/kb/2494162
MPIO failover fails on a computer that is running Windows Server 2008 R2
http://support.microsoft.com/kb/2460971
The MPIO driver fails over all paths incorrectly when a transient single failure occurs in Windows Server 2008 or in Windows Server 2008 R2
http://support.microsoft.com/kb/2522766
Performance decreases in Windows Server 2008 R2 when the Hyper-V role is installed on a computer that uses Intel Westmere or Sandy Bridge processors
http://support.microsoft.com/kb/2517329
Stop error 0x0000007a occurs on a virtual machine that is running on a Windows Server 2008 R2-based failover cluster with a cluster shared volume, and the state of the CSV is switched to redirected access.
http://support.microsoft.com/kb/2494016
Optional Hotfixes
An update is available for Hyper-V Best Practices Analyzer for Windows Server 2008 R2
http://support.microsoft.com/kb/2485986
“0x0000009E” Stop error when you add an extra storage disk to a failover cluster in Windows Server 2008 R2
http://support.microsoft.com/kb/2520235
A virtual machine online backup fails in Windows Server 2008 R2 when the SAN policy is set to Offline All
http://support.microsoft.com/kb/2521348
Cluster node cannot rejoin the cluster after the node is restarted or removed from the cluster in Windows Server 2008 R2
http://support.microsoft.com/kb/2549472
Cluster service stops when an error occurs in the registry replication process of a failover cluster in Windows Server 2008 R2 or in Windows Server 2008
http://support.microsoft.com/kb/2496034
0×20001 Stop error when you start a Linux VM in Windows Server 2008 R2 SP1
http://support.microsoft.com/kb/2550569
A heap memory leak occurs when an application or service queries the MSCluster_Resource WMI class in Windows Server 2008 R2
http://support.microsoft.com/kb/2580360
Cluster service initiates a failover after a delay of about 80 seconds when you shutdown the active node in Windows Server 2008 R2
http://support.microsoft.com/kb/2575625/en-us?sd=rss&spid=14134
New registration entries are added to the Persistent Reservation table when the physical disk resource that is associated with the CSV is taken offline on a Windows Server 2008 R2-based Failover Cluster
http://support.microsoft.com/kb/2579052/en-us?sd=rss&spid=14134
A transient communication failure causes a Windows Server 2008 R2 failover cluster to stop working
http://support.microsoft.com/kb/2550886
Cluster service leaks memory when the service handles state change notifications in Windows Server 2008 R2 or Windows Server 2008
http://support.microsoft.com/kb/2550894
Hyper-V Export function consumes all available memory in Windows Server 2008 or in Windows Server 2008 R2
http://support.microsoft.com/kb/2547551
Microcode update for Intel processors in Windows 7 or in Windows Server 2008 R2
http://support.microsoft.com/kb/2493989
Corrupted VSS snapshot
http://support.microsoft.com/hotfix/KBHotfix.aspx?kbnum=975688&kbln=en-us
FIX: The guest operating system may crash (STOP 0xd) when you perform a live migration of Hyper-V virtual machines in a Windows Server 2008 R2 environment
