Metro Mirror

Metro mirroring is a function of the IBM® System Storage® Server. The data that is stored in IASPs is on disk units that are in the System Storage Server. This solution involves replication at the hardware level to a second storage server that uses IBM System Storage Copy Services. Each storage server is attached to a different IBM i. An IASP is the basic unit of storage for the System Storage Peer-to-Peer Remote Copy (PPRC) function. PPRC provides replication of the IASP to another System Storage Server. IBM i provides a set of functions to combine the PPRC, IASPs, and IBM i cluster resource services for coordinated switchover and failover processing through a device cluster resource group (CRG). You can combine this solution with other System Storage based copy services functions, including switchable LUNs and FlashCopy® for save window reduction.

Metro Mirror replication is done synchronously. You must also be aware of the distance limitations and bandwidth requirements that are associated with transmission times as with any solution when synchronous communications are used.

Characteristics of Metro Mirror
  • IBM System Storage Server solution that is integrated with PowerHA® framework.
  • Second copy of data can be geographically dispersed a short to medium distance.
  • Two System Storage Servers or two datasets on the same System Storage Server are required.
  • Cost is associated with a second set of disk.
  • Offline saves and queries possible while replication is suspended or from a point in time copy of the data.
  • Data resiliency is not maintained while backup dataset is detached. Data resiliency is resumed after resynchronization has completed.
  • Data transmission is a synchronous process. No in-flight data loss is possible.
  • Synchronous data replication process might affect application performance if communications bandwidth is not properly sized or if the distance is too great.
  • No system overhead to run Metro Mirror, it is handled by the storage server.
  • Journaling the objects in the independent disk pool ensures that those changes are forced quickly to disk where they are then replicated to the target system.
  • Replication of the independent disk pool data is at the disk sector level between the disks on the two Storage Servers. All objects in the independent disk pool will be synchronized.
  • Multiple Fibre Channel communication lines available for redundancy and increased bandwidth.