After ESX 3.5 update 3 there was the risk for I/O failure to your SAN.  It presents itself like:

  • VMware ESX or ESXi host might get disconnected from VirtualCenter
  • All paths to the LUNs are in standby state
  • esxcfg-rescan might take a long time to complete or never completes
  • Error messages in vmkernel log

Last Friday VMware published a patch for this problem.

This issue can occur if you’ve got the following:

  • VMware ESX 3.5 U3
  • SAN hardware: Active/Passive and Active/Active arrays (Fibre Channel and iSCSI)
  • Problem occurs when VMFS3 metadata updates are being done at the same time failover to an alternate path occurs for the LUN on which the VMFS3 volume resides

The issue can be resolved with the January 30 patch.  You have to reboot your server for this to work.

Link to the knowledge base article: