Product Model: FAS and AFF systems
Shelf IOM hardware fault due to: reference clock failure.
EMS Event Log:
Wed Apr 20 21:56:35 EDT [Netapp-08: dsa_worker2: ses.status.ModuleError:critical]: DS4486 (S/N SHABC1234000789) shelf 2 on channel 0a SAS expander error for SAS shelf electronics 1: critical status; Reference Clock Failure. This module is on the rear of the shelf at the top center, on shelf module A.
Wed Apr 20 21:56:44 EDT [Netapp-08: statd: monitor.shelf.fault:critical]: Fault reported on disk storage shelf attached to channel 0a. Check fans, power supplies, disks, and temperature sensors.
Also, you might notice all the disks on the shelf showing DIS/CLK under storage-expander within the ASUP.
DIS/CLK = PHY is disabled due to an expander reference clock error.