Symptoms: 
After updating the ESXi Version to 6.5 Update 2, LUNs (seen through SAS Drives) might go missing.

ESXi Version: VMware ESXi 6.5.0 Update 2 build-8935087
Hardware: Dell Inc. PowerEdge R430

Run below command to check the Path Status for the LUN (naa.xxx):
esxcfg-mpath -l

You would see output as below
sas.yyy-naa.xxx
Runtime Name: vmhba#:C#:T#:L#
Device: naa.xxx
Device Display Name: COMPELNT Serial Attached SCSI Disk (naa.xxx)
Adapter: vmhba# Channel: # Target: # LUN: #
Plugin: NMP
State: standby
Transport: sas

Snippet from vmkernel.log
2018-0x-xxTyy:32:00.126Z cpu7:65815)ScsiDeviceIO: 2968: Cmd(0x439500d36dc0) 0x25, CmdSN 0xc789 from world 0 to dev “naa.xxx” failed H:0x5 D:0x0 P:0x0 Invalid sense data: 0x7 0x0 0x0.
2018-0x-xxTyy:32:00.126Z cpu7:65815)WARNING: NMP: nmp_DeviceStartLoop:728: NMP Device “naa.xxx” is blocked. Not starting I/O from device.
2018-0x-xxTyy:32:00.665Z cpu4:66031)WARNING: NMP: nmpDeviceAttemptFailover:603: Retry world restore device “naa.xxx” – no more commands to retry
2018-0x-xxTyy:32:00.665Z cpu1:66030)WARNING: NMP: nmp_SelectPathAndIssueCommand:4633: PSP selected path “vmhba#:C#:T#:L#” in a bad state (standby) on device “naa.xxx”.

2018-0x-xxTyy:32:40.129Z cpu0:92129)WARNING: ScsiDeviceIO: 10131: READ CAPACITY on device “naa.xxx” from Plugin “NMP” failed. I/O error

Above snippet suggests that there is no active path to the LUN, therefore PSP is not able to select a path to issue IOs.

Check below points & update Driver or Firmware for vmhba if it is not up to date.

  • VMware KB to determine currently installed HBA Driver & Firmware on ESXi Host
  • VMware HCL Link for information related to compatible Driver & Firmware for the HBA (vmhba)


Resolution:

ESXi would probe the path, however, it doesn’t have any control over it. The Storage Array responds as PSP selected path “vmhba#:C#:T#:L#” in a bad state (standby) on device “naa.xxx” & there is no active path available. Since ESXi doesn’t have control over it, it can’t change the path from standby to active.

To address the above issue, need to engage Server/Hardware Vendor or the SAS Vendor to understand why is the Path showing up in Standby State.