This e-Learning module will help you learn more about Metro Mirror and Global Mirror, which are two types of copy services offered with the Lenovo Storage V series products. These copy services help administrators migrate, back up, and recover data by creating synchronous and asynchronous copies of volumes. You will also learn how to use Metro Mirror and Global Mirror for disaster recovery, and some best practices. Note that the Metro Mirror and Global Mirror services only apply to block volumes.
To access Metro and Global Mirror functions, you first need to purchase a license. Then, you create a Metro Mirror or Global Mirror relationship between two volumes. If the volumes belong to different systems, you will need to establish a partnership first. Note that you can perform Metro and Global Mirror functions on block volumes of all supported systems.
Metro Mirror is a copy service that provides a continuous, synchronous mirror of one volume to a second volume. The different systems can be up to 300 kilometers apart, so by using Metro Mirror you can make a copy to a location off-site or across town. Because the mirror is updated in real time, no data is lost if a failure occurs. Metro Mirror is generally used for disaster-recovery purposes, where it is important to avoid data loss.
Global Mirror is a copy service that is very similar to Metro Mirror. Both provide a continuous mirror of one volume to a second volume. But with Global Mirror, the copy is asynchronous. You do not have to wait for the write to the secondary system to complete. For long distances, performance is improved compared to Metro Mirror. However, if a failure occurs, you might lose data. Global Mirror uses one of two methods to replicate data. Multicycling Global Mirror is designed to replicate data while adjusting for bandwidth constraints, and is appropriate for environments where it is acceptable to lose a few minutes of data if a failure occurs. For environments with higher bandwidth, noncycling Global Mirror can be used so that less than a second of data is lost if a failure occurs. Global Mirror works well for data protection and migration when recovery sites are more than 300 kilometers away.
Before you establish a Metro Mirror or Global Mirror relationship between two systems, you need to create a partnership, and configure the background copy bandwidth for that partnership. The background copy bandwidth is the maximum bandwidth that the system is allowed to use for initial synchronization, or re-synchronization, of mirrored volumes. From the Copy Services icon, choose Partnerships. Any partnerships that are already established on the system are displayed. Click New Partnership, and select the remote system that you would like to partner with the system that you are managing. Enter a value for the intersystem link bandwidth, and click Create. Then, start a management GUI session on the remote system, and repeat this step to complete partnership creation.
You can establish Metro Mirror or Global Mirror relationships individually, or as part of a consistency group. To create an individual relationship, go to the Remote Copy panel and select New Relationship. Select the type of relationship, then indicate whether the auxiliary volume resides on the same system or on a different system. Select the master and auxiliary volumes for the relationship, and click Add. You can use this panel to add more than one relationship. Indicate whether the volumes have already been synchronized and whether to begin copying immediately. Click Finish to establish the relationship. You can select Details to view the CLI commands as the task completes.
You can group Metro Mirror or Global Mirror relationships into a consistency group so that they can be updated at the same time. A command that is issued to the consistency group is simultaneously applied to all of the relationships in the group. To create a Metro Mirror or Global Mirror relationship within a consistency group, select New Consistency Group from the Remote Copy panel. Enter a name for your consistency group, indicate whether the master and auxiliary volumes reside on the same system or on different systems, and indicate whether to add any relationships to the group at this time. If you select to create an empty consistency group, click Finish. Otherwise, follow the online instructions to add new Metro Mirror or Global Mirror relationships to the consistency group.
You can use the Actions menu to start or stop a Metro Mirror or Global Mirror operation for a consistency group. You can also switch the relationship to change the master copy site. If a relationship is not part of a consistency group, you can select the relationship, then right-click to start or stop the operation.
You can establish multiple partnerships to assist with disaster recovery and data migration. For example, you could set up a system at your company headquarters in New York, and set up a system in each of your company field offices in Orlando, Boston, and Baltimore. You want the New York system to serve as a central disaster-recovery site for the field offices, so you establish three partnerships among these four sites. Then, if one of the field offices experiences data loss, you can use the established partnership with the central site for data recovery.
Here is another example. You could have a production site in London and a data center in Madrid, which provides disaster recovery. You need to migrate the data center to a site in Frankfurt, so you establish three partnerships among the three systems. Then, your production site in London can continue to operate as you migrate data from the Madrid data center over to the new Frankfurt data center.
Global Mirror is a useful feature for high availability and disaster recovery. For example, your company could have a main site and a disaster-recovery site in the same city. If a storm came through and caused significant flooding, it could lead to the loss of critical data. To prevent this from happening, you could use Global Mirroring, and keep your disaster-recovery site in another city or even another country.
If an outage occurs, your secondary site can temporarily become your primary site. After the damaged systems are restored, synchronization between the sites can be initiated. Global Mirror synchronizes only the data that has changed since the outage occurred. After all the changed data has been replicated, you can reverse the direction back to normal. Or, you can choose to permanently keep your secondary site as your primary site.
A two-site disaster-recovery solution not only can improve your application availability in case of disaster, but it can also improve availability during a planned outage. Moving an active application to a secondary site because of a planned outage is a useful way to test whether your disaster-recovery solution is configured correctly. To ensure that your disaster-recovery solution is reliable, you should perform regular tests.
When using Global Mirror, it is important to keep your system properly configured. To help you do this, follow these best practices: Use the IBM Tivoli(R) Storage Productivity Center product or an equivalent performance analysis tool to monitor your SAN environment. Analyze the performance statistics on the primary and secondary sites to determine the peak application write workload that the link and storage must support. Gather statistics over a typical application I/O workload cycle. This will help ensure that the link and the storage at the secondary site can sustain the primary site workload. Set the background copy rate to a value that supports the intersystem link and the back-end storage controllers at the remote system. If the value cannot support the link and storage, the secondary site can become overloaded and no longer support the information demand. Do not use cache-disabled volumes in Global Mirror relationships. The performance of cache-disabled volumes is not suitable for Global Mirror workloads.
This e-Learning module introduced you to Metro Mirror and Global Mirror, and described related interface tasks and usage scenarios. To learn more, see the other e-Learning modules and topics in this information center.