One of the main reasons for using Copy Services functions is to
prepare for a possible disaster by backing up, copying, and mirroring your
data both at the local (production) and remote sites.
Having a disaster recovery plan can ensure that critical data is recoverable
at the time of a disaster. Because most disasters are unplanned, your disaster
recovery plan must provide a way that allows you to recover your applications
quickly, and more importantly, to access your data. Consistent data to the
same point-in-time across all storage units is vital before you can recover
your data at a backup (normally your remote) site.
Most users use a combination of remote mirror and copy and
point-in-time copy (FlashCopy) features to form a comprehensive enterprise
solution for disaster recovery. In an event of a planned event or unplanned
disaster, you can use failover and failback modes as part of your recovery
solution. Failover and failback modes help to reduce the time that is required
to synchronize remote mirror and copy volumes
after you switch between the local (or production) and the remote sites during planned and
unplanned outages. Although failover transmits no data, it changes the status
of a device, and the status of the secondary volume changes to a suspended
primary volume. The Failback command transmits data and can go in either direction
depending on which device the Failback command is issued to.
Recovery procedures that include failover and failback modes use
remote mirror and copy functions, such as
Metro Mirror,
Global Copy,
Global Mirror,
Metro/Global Mirror, and FlashCopy.
Note: See the IBM® System Storage™ DS6000™ Command-Line
Interface User's Guide for
specific disaster recovery tasks.
Data consistency can be achieved using the following methods:
- Manually using external software (without Global Mirror)
- If you use Metro Mirror, Global Copy,
and FlashCopy functions to create a consistent and restartable copy at your
recovery site, you must do a manual and periodic suspend operation at your
local site. This means using freeze and run commands together with
external automated software and then using the FlashCopy function to make
a consistent copy of your target volume for backup or recovery purposes.
(Automation software is not provided with the storage unit; it must be supplied
by the user.)
Note: Freezing of the data is done at the same point-in-time
across all links and all storage units.
- Automatically (with Global Mirror and
FlashCopy)
- If you use a two-site Global Mirror configuration, the process to create a consistent and restartable
copy at your remote
site is done using an automated process, with minimal or no interruption to
your applications. Global Mirror operations automate the process of continually
forming consistency groups. It combines Global Copy and FlashCopy operations
to provide consistent data at the remote site. A master storage unit (along
with subordinate storage units) internally manages data consistency using
consistency groups within a Global Mirror configuration. Consistency groups
can be created many times per hour to increase the currency of data that is
captured in the consistency groups at the remote site.
Note: A consistency
group is a collection of volumes (grouped in a session) across multiple storage
units that are managed together in a session during the creation of consistent
copies of data. The formation of these consistency groups is coordinated by
the master storage unit, which sends commands over remote mirror and copy
links to its subordinate storage units.
In a two-site Global Mirror configuration, if you have a disaster at your local site and have to
start production at your remote site, you can use the consistent point-in-time
data from the consistency group at your remote site to recover when the local
site is operational.