Remote Copy; Ip Replication - IBM Storwize V5010 Manual

1.7.7 Remote Copy

Remote Copy can be implemented in one of two modes, synchronous or asynchronous.
With the IBM Storwize V5000 Gen2, Metro Mirror and Global Mirror are the IBM branded
terms for the functions that are synchronous Remote Copy and asynchronous Remote Copy.
By using the Metro Mirror and Global Mirror copy services features, you can set up a
relationship between two volumes so that updates that are made by an application to one
volume are mirrored on the other volume. The volumes can be in the same system or on two
different systems.
For both Metro Mirror and Global Mirror copy types, one volume is designated as the primary
and the other volume is designated as the secondary. Host applications write data to the
primary volume, and updates to the primary volume are copied to the secondary volume.
Normally, host applications do not perform I/O operations to the secondary volume.
The Metro Mirror feature provides a synchronous copy process. When a host writes to the
primary volume, it does not receive confirmation of I/O completion until the write operation
completes for the copy on the primary and secondary volumes. This design ensures that the
secondary volume is always up-to-date with the primary volume if a failover operation must be
performed.
The Global Mirror feature provides an asynchronous copy process. When a host writes to the
primary volume, confirmation of I/O completion is received before the write operation
completes for the copy on the secondary volume. If a failover operation is performed, the
application must recover and apply any updates that were not committed to the secondary
volume. If I/O operations on the primary volume are paused for a brief time, the secondary
volume can become an exact match of the primary volume.
Global Mirror can operate with or without cycling. When it is operating without cycling, write
operations are applied to the secondary volume as soon as possible after they are applied to
the primary volume. The secondary volume is less than 1 second behind the primary volume,
which minimizes the amount of data that must be recovered in a failover. However, this
approach requires that a high-bandwidth link is provisioned between the two sites.
When Global Mirror operates with cycling mode, changes are tracked and where needed
copied to intermediate change volumes. Changes are transmitted to the secondary site
periodically. The secondary volumes are much further behind the primary volume, and more
data must be recovered in a failover. Because the data transfer can be smoothed over a
longer time period, lower bandwidth is required to provide an effective solution.
For more information about the IBM Storwize V5000 Gen2 copy services, see Chapter 10,
"Copy services" on page 485.
The IBM Remote Copy feature is licensed for each enclosure.

1.7.8 IP replication

IP replication
capability is available as a chargeable option on all Storwize family systems.
The function is transparent to servers and applications in the same way that traditional Fibre
Channel-based mirroring is transparent. All remote mirroring modes (Metro Mirror, Global
Mirror, and Global Mirror with Change Volumes) are supported.
enables the use of lower-cost Ethernet connections for remote mirroring. The
Chapter 1. Overview of the IBM Storwize V5000 Gen2 system
31