Working with Permanent Device Loss

In some cases a permanent device loss (PDL) might occur.

With earlier ESXi releases, an APD (All Paths Down) event results when the LUN becomes unavailable. The event is difficult for administrators because they do not have enough information about the state of the LUN to know which corrective action is appropriate.

In ESXi 5.0, the ESXi host can determine whether the cause of an APD event is temporary, or whether the cause is PDL. A PDL status occurs when the storage array returns SCSI sense codes indicating that the LUN is no longer available or that a severe, unrecoverable hardware problem exist with it. ESXi has an improved infrastructure that can speed up operations of upper-layer applications in a device loss scenario.

Important: Do not plan for APD or PDL events, for example, when you want to upgrade your hardware. Instead, perform an orderly removal of LUNs from your ESXi server, which is described in Detach a Device and Remove a LUN, perform the operation, and add the LUN back.