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If the device returns from the PDL condition, the host can discover it, but treats it as a new device. Data
consistency for virtual machines on the recovered device is not guaranteed.
Note When a device fails without sending appropriate SCSI sense codes or an iSCSI login rejection, the
host cannot detect PDL conditions. In this case, the host continues to treat the device connectivity
problems as APD even when the device fails permanently.
Permanent Device Loss and SCSI Sense Codes
The following VMkernel log example of a SCSI sense code indicates that the device is in the PDL state.
H:0x0 D:0x2 P:0x0 Valid sense data: 0x5 0x25 0x0 or Logical Unit Not Supported
Permanent Device Loss and iSCSI
On iSCSI arrays with a single LUN per target, PDL is detected through iSCSI login failure. An iSCSI
storage array rejects your host's attempts to start an iSCSI session with a reason Target Unavailable.
As with the sense codes, this response must be received on all paths for the device to be considered
permanently lost.
Permanent Device Loss and Virtual Machines
After registering the PDL state of the device, the host closes all I/O from virtual machines. vSphere HA
can detect PDL and restart failed virtual machines. For more information, see Device Connectivity
Problems and High Availability.
Performing Planned Storage Device Removal
When a storage device is malfunctioning, you can avoid permanent device loss (PDL) conditions or all
paths down (APD) conditions. Perform a planned removal and reconnection of a storage device.
Planned device removal is an intentional disconnection of a storage device. You might also plan to
remove a device for such reasons as upgrading your hardware or reconfiguring your storage devices.
When you perform an orderly removal and reconnection of a storage device, you complete a number of
tasks.
Task Description
Migrate virtual machines from the device you plan to detach. vCenter Server and Host Management
Unmount the datastore deployed on the device. See Unmount Datastores.
Detach the storage device. See Detach Storage Devices.
For an iSCSI device with a single LUN per target, delete the static target entry from
each iSCSI HBA that has a path to the storage device.
See Remove Dynamic or Static iSCSI
Targets.
Perform any necessary reconfiguration of the storage device by using the array
console.
See your vendor documentation.
Reattach the storage device. See Attach Storage Devices.
Mount the datastore and restart the virtual machines. See Mount Datastores.
vSphere Storage
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