PowerStore: PUHC failed with "The system encountered unexpected backend errors. Please contact support"

During a PowerStoreOS Code upgrade, the Pre-Upgrade Health Check has failed.

From the PowerStore node journal log, the cause is logged.

Sep 28 22:56:54.847708 ASSET-A control-path[124493]: 2021-09-28 22:56:54.847 [NDU] [INFO] [com.emc.cyclone.contexts.infrastructure.ndu.application.NDUCommonUtil.ApplianceUpgradeUtil|vert.x-eventloop-thread-0] [72fee6ed-bc69-47f6-a4e3-05d8ac9deb1d|9b3b14a3-e90d-4fee-914d-1ac253b28bb1|fetchApplianceSessionInfo] Platform request to fetch appliance session id completed successfully1
 Sep 28 22:56:54.847772 ASSET-A control-path[124493]: 2021-09-28 22:56:54.847 [NDU] [INFO] [com.emc.cyclone.contexts.infrastructure.ndu.application.NDUCommonUtil.ApplianceUpgradeUtil|vert.x-eventloop-thread-0] [72fee6ed-bc69-47f6-a4e3-05d8ac9deb1d|9b3b14a3-e90d-4fee-914d-1ac253b28bb1|fetchApplianceSessionInfo] Is rollback failed state on the appliance upgrade session is null
 Sep 28 22:56:54.954970 ASSET-A control-path[124493]: 2021-09-28 22:56:54.954 [NDU] [INFO] [com.emc.cyclone.contexts.infrastructure.ndu.application.NDUCommonUtil.AwaitResponsesFromPlatformUtil|vert.x-eventloop-thread-0] [72fee6ed-bc69-47f6-a4e3-05d8ac9deb1d|9b3b14a3-e90d-4fee-914d-1ac253b28bb1|prestageHandleResponse] Platform request completed successfully
 Sep 28 22:57:24.996368 ASSET-A control-path[124493]: 2021-09-28 22:57:24.996 [NDU] [ERROR] [com.emc.cyclone.contexts.infrastructure.services.platform.gateway.application.upgrade.service.cycloneCommandService.PrestageUpgradePackageAS|vert.x-eventloop-thread-0] [72fee6ed-bc69-47f6-a4e3-05d8ac9deb1d]
 Prestage failed: (with error 'java.lang.Exception: ERROR: 15G free space is required. Clean up the space under /cyc_cfs and try again.

Explanation
The cyc_fs file system is used to store support materials diagnostic files and the space consumed by these is normally automatically managed. In a few rare occasions, too many support materials were retained causing free space in cyc_fs to be low.

Use the PowerStore Manager UI or the service shell script svc_dc to remove older data collects to free up space in cyc_fs.