For this reason, it is highly advisable to create a FlashCopy of the secondary volume  before restarting the relationship. When started, the FlashCopy provides a consistent copy  of the data, even while the Global Mirror relationship is copying. If the Global Mirror  relationship does not reach the Synchronized state (if, for example, the intercluster link  experiences further persistent I/O errors), the FlashCopy target can be used at the  secondary site for disaster recovery purposes. Example 4-2 shows a best-guess bandwidth sizing formula, assuming that the  write/change rate is consistent. IBM FlashSystem 9100 supports setting up a Simple Mail Transfer Protocol (SMTP) mail  server for alerting the IBM Support Center of system incidents that might require a service  event. This is the  call home  option. You can enable this option during the setup. Tip:  Setting up call home involves providing a contact that is available 24 x 7 if a serious  call home issue occurs. IBM support strives to report any issues to clients in a timely  manner; having a valid contact is important to achieving service level agreements (SLAs). 4.4.6 Call Home option GLYPH<SM590000> Do not propose Global Mirror if the data change rate exceeds the communication  bandwidth, or if the round-trip latency exceeds 80 - 120 ms. A greater than 80 ms  round-trip latency requires Solution for Compliance in a Regulated Environment and  request for price quotation (SCORE/RPQ) submission. GLYPH<SM590000> You must also consider the initial sync and resync workload. The Global Mirror  partnership’s background copy rate must be set to a value that is appropriate to the link  and secondary back-end storage. The more bandwidth that you give to the sync and  resync operation, the less workload can be delivered by the IBM FlashSystem 9100 for the  regular data traffic. GLYPH<SM590000> If the network bandwidth is too small to handle the traffic, the application write I/O  response times might be elongated. For the IBM FlashSystem 9100, Global Mirror must  support short-term  Peak Write  bandwidth requirements. GLYPH<SM590000> If compression is available on routers or wide area network (WAN) communication  devices, smaller pipelines might be adequate. Note that workload is probably not evenly  spread across 24 hours. If there are extended periods of high data change rates, consider  suspending Global Mirror during that time frame. Amount of write data within 24 hours times 4 to allow for peaks Translate into MB/s to determine WAN link needed Example: 250 GB a day 250 GB * 4 = 1 TB 24 hours * 3600 secs/hr. = 86400 secs 1,000,000,000,000/ 86400 = approximately 12 MB/s, Which means OC3 or higher is needed (155 Mbps or higher) Example 4-2 Bandwidth sizing GLYPH<SM590000> If you plan to use a Fibre Channel over IP (FCIP) intercluster link, it is extremely important  to design and size the pipe correctly. Chapter 4. Planning  91