Metro Mirror and Global Mirror Data Copy

Simply put, Metro Mirror creates a synchronous copy of your data in another location and Global Mirror creates an asynchronous copy of your data in another location.

  • Synchronous: happening, existing, or arising at precisely the same time
  • Asynchronous: not synchronous or (as between computers) in which there is no timing requirement for transmission and in which the start of each character is individually signaled by the transmitting device

Metro Mirror and Global Mirror allow you to set up a relationship between two volumes, where updates made to one are mirrored on the other.
The volumes can be set up on the same or separate system (intrasystem or intersystem).

  • Intrasystem: existing or occurring within one system
  • Intersystem: existing or occurring between separate systems

For disaster recovery, the intersystem is needed so you can put a distance between your data copies.

For bigger data, the SAN fabric to which the systems are attached needs to have proper bandwidth. If you are not sure if you have enough, we can walk you through that.

With the Metro Mirror synchronous copies, the host writes to the primary volume but does not get a confirmation that the write operation is finished until the data is finished being written to the secondary volume.
This makes sure that the data on both volumes is exactly the same.
After the first copy is complete, the Metro Mirror keeps a synchronized copy of the source data at your secondary location all the time.

The Global Mirror is an asynchronous copy process.
When your host writes data to the main volume, you get a confirmation that the write operation is finished before the write operation has finished on your secondary volume.

So, for Global, nothing happens remotely until the data is successfully written at home.

In Storwize, you can go from Metro to Global without recreating your original relationship from home to remote. This would come in handy if the latency of the link from home to remote has a negative impact on your host.

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