When something wrong happens on your SCSI network (FC, iSCSI, infiniband, FCoE, etc…), error messages rise in ESXi logs.
When a SCSI target device returns a check condition in response to a command, the initiator usually then issues a SCSI Request Sense command. This process is part of a SCSI protocol called Contingent Allegiance Condition. The target will respond to the Request Sense command with a set of SCSI sense data which includes three fields giving increasing levels of detail about the error
2015-02-17T08:06:35.915Z esx.vmware.com vmkernel: cpu29:1557927)ScsiDeviceIO: 2324: Cmd(0x4124810c1c80) 0xfe, CmdSN 0x81a827 from world 7160931 to dev "naa.60a9800044344f7a765d455872413370" failed H:0x0 D:0x2 P:0x0 Valid sense data: 0xa 0xd 0x2.
The SenseData dashboard comes in to help: