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. 

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. 

Example 4-2 shows a best-guess bandwidth sizing formula, assuming that the write/change rate is consistent. 

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) 

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. 

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> 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> 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. 

## 4.4.6 Call Home option 

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). 

