Dell EMC Unity : When a disk fails in a Dynamic pool, array performance can be impacted (Dell EMC Correctable)

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. 

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.

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 "<name of pool>" show -detail

Example:

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 "<pool name>"

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."

Dell EMC Unity 300F, Dell EMC Unity 350F, Dell EMC Unity XT 380F, Dell EMC Unity 400F, Dell EMC Unity 450F, Dell EMC Unity XT 480F, Dell EMC Unity 600F, Dell EMC Unity 650F, Dell EMC Unity XT 680F, Dell EMC Unity XT 880F , Dell EMC Unity Family |Dell EMC Unity All Flash ... View More View Less