Symptoms

Dynamic Pools can use allocated space in the pool to rebuild. When the rebuild started there was complete data unavailability until that failed disk was replaced and the rebuild completed. When the rebuild completed performance returned to normal. A Dynamic pool had a drive fail. The pool started to rebuild to the spare space in the pool. That affected the array performance to the point that data unavailability occurred.

Cause

The root cause of the problem is that host I/Os slow down because of the resources being used by the SP. The dynamic pool rebuild/reshuffle operation consumes so many resources that there is not enough left over for host I/O.

Resolution

Contact Dell EMC Technical Support or your Authorized Service Representative, and quote this Knowledgebase article ID. This will be addressed in a future release of Unity Code.We can confirm the issue using the following steps:1. Establish an SSH session to the array. 2. Verify using the below command to determine if the pool in question is Dynamic: Command >> uemcli /stor/config/pool -name "" show -detailExample: 15:25:23 service@APMx spb:~/user> uemcli /stor/config/pool -name "My Dynamic Pool" show -detail Storage system address: 127.0.0.1 Storage system port: 443 HTTPS connection 1: ID = pool_4 Type = Dynamic Name = My Dynamic Pool Description = Total space = 6176968278016 (5.6T) 3. Verify that a rebuild is in progress with the below command: Command >> cat /EMC/C4Core/log/EMCSystemLogBackup.log | grep -i ""Example: 15:26:23 service@APMx spb:~/user> cat /EMC/C4Core/log/EMCSystemLogBackup.log | grep -i "My Dynamic Pool" "2019-04-13T18:40:02.213Z" "spb@APMx" "Neo_CEM" "23864" "N/A" "WARN" "14:6032d" :: "Storage pool My Dynamic Pool is degraded." :: Category=User Component=Health TimeZone=UTC "2019-04-13T18:45:12.766Z" "spb@APMx" "Neo_CEM" "23864" "N/A" "WARN" "14:60343" :: "Storage pool My Dynamic Pool is rebuilding due to the loss of a drive." :: Category=User Component=Health TimeZone=UTC As highlighted above the command will provide output stating that the Pool is Degraded as well as it reports the "Pool is rebuilding."

Support Cases