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

vSphere StoragePerform Adapter Rescan in the vSphere Web ClientWhen you make changes in your SAN configuration and these changes are isolated to storage accessedthrough a specific adapter, perform rescan for only this adapter.Procedure1 Browse to the host in the vSphere Web Client navigator.2 Click the Manage tab, and click Storage.3 Click Storage Adapters, and select the adapter to rescan from the list.4 Click Rescan Adapter.Change the Number of Scanned LUNs in the vSphere Web ClientBy default, the VMkernel scans for LUN 0 to LUN 255 for every target (a total of 256 LUNs). You can modifythe Disk.MaxLUN parameter to improve LUN discovery speed.IMPORTANT You cannot discover LUNs with a LUN ID number that is greater than 255.Reducing the value can shorten rescan time and boot time. However, the time to rescan LUNs might dependon other factors, including the type of storage system and whether sparse LUN support is enabled.Procedure1 Browse to the host in the vSphere Web Client navigator.2 Click the Manage tab, and click Settings.3 Under System, click Advanced System Settings.4 Under Advanced System Settings, select Disk.MaxLUN and click the Edit icon.5 Change the existing value to the value of your choice, and click OK.The value you enter specifies the LUN after the last one you want to discover.For example, to discover LUNs from 0 through 31, set Disk.MaxLUN to 32.Identifying Device Connectivity ProblemsWhen your ESXi host experiences a problem while connecting to a storage device, the host treats theproblem as permanent or temporary depending on certain factors.Storage connectivity problems are caused by a variety of reasons. Although ESXi cannot always determinethe reason for a storage device or its paths being unavailable, the host differentiates between a permanentdevice loss (PDL) state of the device and a transient all paths down (APD) state of storage.Permanent Device Loss(PDL)All Paths Down (APD)A condition that occurs when a storage device permanently fails or isadministratively removed or excluded. It is not expected to becomeavailable. When the device becomes permanently unavailable, ESXi receivesappropriate sense codes or a login rejection from storage arrays, and is ableto recognize that the device is permanently lost.A condition that occurs when a storage device becomes inaccessible to thehost and no paths to the device are available. ESXi treats this as a transientcondition because typically the problems with the device are temporary andthe device is expected to become available again.124 VMware, Inc.