Scenario: Switched disk with geographic mirroring
This scenario describes an 
PowerHA®
solution
that uses switched disks with geographic mirroring in a three-node
cluster. This solution provides both disaster recovery and high availability.
Overview
At the production site (Uptown), switched disks are
used to move independent disk pools between two nodes. The solution
also uses geographic mirroring to generate a copy of the independent
disk at a second site (Downtown). Thus, this solution provides both
disaster recovery and high availability. The benefits of this solution
are essentially the same as the basic switched disk solution with
the added advantage of providing disaster recovery to application
data by duplicating that data at another location. The production
site (Uptown) has an independent disk pool that can be switched between
logical partitions to provide high availability with fast switchover
times for planned outages, such as applying fixes. This solution also
provides disaster recovery with geographic mirroring.
Geographic mirroring is a PowerHA replication technology
where data is mirrored to a copy of the independent disk pool at the
remote location. Data from the independent disk pool at the production
site (Uptown) is mirrored to an independent disk pool on the backup
site (Downtown). This solution provides a simple and less expensive
alternative to external storage-based solutions, such as IBM®System Storage® Global Mirror and Metro Mirror. However, geographic mirroring
does not offer all the performance options that the external storages
solutions provide.
Objectives
This solution has the following advantages:- Provides availability for your business resources during planned outages
- Provides availability for business resources during unplanned outages
- Provides availability for business resources during site-wide disasters
- Enables each site to have a single copy of data, which minimizes the number of disk units that are required
- Enables data to remain current and may not need to be synchronized
- There is no concurrent access to the disk pool. However, you can detach the mirror copy for offline processing of a second copy of the data.
- There is potential performance effects with increased central processing unit (CPU) that is required to support geographic mirroring
- Consider using redundant communication paths and adequate bandwidth
Details
This graphic illustrates this solution:
Configuration steps
Complete the following steps to configure the high
availability technologies that are associated with this scenario using
the PowerHA graphical
interface:- Make hardware switchable
- Complete planning checklist for clusters
- Create a cluster
- Create a cluster administrative domain
- Start a cluster administrative domain
- Create an independent ASP
- Add monitored resource entries
- Make the independent ASP highly available
- Configure geographic mirroring
- Vary on the independent ASP
- Perform a switchover to test your high-availability solution.
Complete the following steps to configure
the high availability technologies that are associated with this scenario using
commands:- Make hardware switchable
- Complete planning checklist for clusters
- Create a cluster
- Add a node
- Start a node
- Add a node to a device domain
- Create a device CRG
- Create cluster administrative domain
- Start cluster administrative domain
- Create an independent disk pool using Configure Device ASP.
- Add monitored resource entries
- Configure geographic mirroring
- Starting
a device CRG
- Use Vary Configuration to make the disk pool available.
- Perform a switchover to test configuration.