What are VMware APD and PDL?

Hi Muhammad,

Have a nice day!

Permanent Device Loss (PDL):

1. A datastore is shown as unavailable in the Storage view.

2. A storage adapter indicates the Operational State of the device as Lost Communication.

All-Paths-Down (APD):

1. A datastore is shown as unavailable in the Storage view.

2. A storage adapter indicates the Operational State of the device as Dead or Error.

Thank you.

Dear Muhammad,

There are two distinct states a device can be in when storage connectivity is lost; All Paths Down (APD) or Permanent Device Loss (PDL). For each of these states:

All Paths Down (APD) is a condition where all paths to the storage device are lost or the storage device is removed. The state is caused because the change happens in an uncontrolled manner, and the VMkernal core storage stack does not know how long the loss of access to the device will last. The APD is a condition that is treated as temporary (transient), since the storage device might come back online; or it could be permanent, which is referred to as a Permanent Device Loss (PDL).Till 5.x there was no support for handling APD state.

PDL (Permanent Device Loss) Esxi considers device loss permanent. It can be caused by making a LUN inaccessible to a host, either by unmapping or deleting it. In this case, the storage array informs the host of a PDL state through a SCSI command response. The removal is considered permanent when all paths have the PDL error.

I hope this clears your question.