Figure 5-26 shows the orders of magnitude of difference between the link bandwidths. It is  easy to see how  1920  errors can arise when your bandwidth is insufficient. Never use a  TCP/IP ping to measure RTT for FCIP traffic. In Figure 5-26, the amount of time in microseconds that is required to transmit a packet  across network links of varying bandwidth capacity is compared. The following packet sizes  are used: Finally, your path maximum transmission unit (MTU) affects the delay that is incurred to get a  packet from one location to another location. An MTU might cause fragmentation, or be too  large and cause too many retransmits when a packet is lost. After a 1920 error occurs, the Global Mirror auxiliary volumes are no longer in a  Consistent  Synchronized  state. You must establish the cause of the problem and fix it before you restart  the relationship.  When the relationship is restarted, you must resynchronize it. During this period, the data on  the Metro Mirror or Global Mirror auxiliary volumes on the secondary system is inconsistent,  and your applications cannot use the volumes as backup disks. To address this data  consistency exposure on the secondary system, a FlashCopy of the auxiliary volumes can be  created to maintain a consistent image until the Global Mirror (or the Metro Mirror)  relationships are synchronized again and back in a consistent state.  IBM Spectrum Virtualize provides the Remote Copy  Consistency Protection  feature that  automates this process. When Consistency Protection is configured, the relationship between  the primary and secondary volumes does not go in to the  Inconsistent copying  status once  restarted. Instead, the system uses a secondary  change volume  to automatically copy the  previous consistent state of the secondary volume.  250  IBM System Storage SAN Volume Controller, IBM Storwize V7000, and IBM FlashSystem 7200 Best  Recovery after 1920 errors GLYPH<SM590000> 64 bytes: The size of the common ping packet GLYPH<SM590000> 1500 bytes: The size of the standard TCP/IP packet GLYPH<SM590000> 2148 bytes: The size of an FC frame Figure 5-26 Effect of packet size (in bytes) versus the link size