ESX and disk issues

ESX 4 & 5: Resolving SCSI reservation conflicts
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1002293
In this KB article is described the process how to find which ESX host has SCSI reservation on LUN

ESX 5: Vmware vSphere 5 dead LUN and pathing issues and resultant SCSI errors
http://raj2796.wordpress.com/2012/03/14/vmware-vsphere-5-dead-lun-and-pathing-issues-and-resultant-scsi-errors/

All ESX versions: After repeated SAN path failovers, operations that involve VMFS changes might fail for all hosts accessing a particular LUN
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1009899

ESX 4.x: ESX/ESXi hosts in APD may appear Not Responding in vCenter Server
http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1030980

ESX 4.1: Virtual machines stop responding when any LUN on the host is in an all-paths-down (APD) condition
http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&externalId=1016626

ESX 5.1 has significant improvements with APD a PDL
http://www.vmware.com/files/pdf/techpaper/Whats-New-VMware-vSphere-51-Storage-Technical-Whitepaper.pdf