When looking at the port-level statistics, high values on ports used for messages to nodes  in the same system are much more concerning than those on ports that are used for  messages to nodes in other systems. This value is the average response time in milliseconds for write operations to the  back-end storage. This time might include several physical I/O operations, depending on  the type of RAID architecture.  Poor back-end performances on secondary system is a frequent cause of 1920 errors,  while it is not so common for primary systems. Exact values to watch out for depend on  the storage technology, but usually the response time should be less than 50 ms. A longer  response time can indicate that the storage controller is overloaded. If the response time  for a specific storage controller is outside of its specified operating range, investigate for  the same reason. The causes of 1920 errors might be numerous. To fully understand the underlying reasons for  posting this error, consider the following components that are related to the remote copy  relationship: A successful diagnosis depends on the collection of the following data at both systems: 208  IBM FlashSystem 9200 and 9100 Best Practices and Performance Guidelines GLYPH<SM590000> Back-end Write Response Time GLYPH<SM590000> The intersystem connectivity network GLYPH<SM590000> Primary storage and remote storage  GLYPH<SM590000> IBM FS9100 node canisters  GLYPH<SM590000> Storage area network GLYPH<SM590000> The  snap  command with  livedump  (triggered at the point of failure) GLYPH<SM590000> I/O Stats running (if possible) GLYPH<SM590000> IBM Spectrum Control performance statistics data (if possible) GLYPH<SM590000> The following information and logs from other components: – Intersystem network and switch details: GLYPH<129> Technology  GLYPH<129> Bandwidth GLYPH<129> Typical measured latency on the Intersystem network GLYPH<129> Whether trunking is enabled GLYPH<129> Distance on all links (which can  take multiple paths for redundancy) GLYPH<129> How the link interfaces with the two SANs GLYPH<129> Whether compression is enabled on the link GLYPH<129> Whether the link dedicated or shared; if so, the resource and amount of those  resources they use GLYPH<129> Switch Write Acceleration  to check with IBM for compatibility or known limitations GLYPH<129> Switch Compression, which should be tr ansparent but complicates the ability to  predict bandwidth – Storage and application: GLYPH<129> Specific workloads at the time of 1920 errors, which might not be relevant,  depending upon the occurrence of the 1920 errors and the volumes that are  involved Data collection for diagnostic purposes  Focus areas for 1920 errors