vsphere-esxi-vcenter-server-55-storage-guide

Chapter 15 Managing Storage DevicesAttach Storage DevicesReattach a storage device that you previously detached.Procedure1 In the vSphere Web Client, display storage devices.2 Select the detached storage device and click the Attach icon.The device becomes accessible.Recovering From PDL ConditionsAn unplanned permanent device loss (PDL) condition occurs when a storage device becomes permanentlyunavailable without being properly detached from the ESXi host.The following items in the vSphere Web Client indicate that the device is in the PDL state:• The datastore deployed on the device is unavailable.• Operational state of the device changes to Lost Communication.• All paths are shown as Dead.• A warning about the device being permanently inaccessible appears in the VMkernel log file.To recover from the unplanned PDL condition and remove the unavailable device from the host, you needto perform a number of tasks.1 Power off and unregister all virtual machines that are running on the datastore affected by the PDLcondition.2 Unmount the datastore.See “Unmount VMFS or NFS Datastores,” on page 145.3 Perform a rescan on all ESXi hosts that had access to the device.See “Perform Storage Rescan in the vSphere Web Client,” on page 123.NOTE If the rescan is not successful and the host continues to list the device, some pending I/O or activereferences to the device might still exist. Check for virtual machines, templates, ISO images, raw devicemappings, and so on that might still have an active reference to the device or datastore.Handling Transient APD ConditionsA storage device is considered to be in the all paths down (APD) state when it becomes unavailable to yourESXi host for an unspecified period of time.The reasons for an APD state can be, for example, a failed switch or a disconnected storage cable.In contrast with the permanent device loss (PDL) state, the host treats the APD state as transient and expectsthe device to be available again.The host indefinitely continues to retry issued commands in an attempt to reestablish connectivity with thedevice. If the host's commands fail the retries for a prolonged period of time, the host and its virtualmachines might be at risk of having performance problems and potentially becoming unresponsive.To avoid these problems, your host uses a default APD handling feature. When a device enters the APDstate, the system immediately turns on a timer and allows your host to continue retrying nonvirtualmachine commands for a limited time period.VMware, Inc. 127