HP XP7 Continuous Access Journal User Guide (TK911-96002)

3 Planning volumes, XP7 systems
This chapter provides information and instructions for planning Continuous Access Journal volumes,
XP7 systems, and other important requirements and restrictions.
Plan and design workflow
Planning the Continuous Access Journal system is tied to your organization’s business requirements
and production system workload. This means defining business requirements for disaster downtime
and measuring the amount of changed data your storage system produces over time. With this
information, you can calculate the size of journal volumes and the amount of bandwidth required
to transfer update data over the data path network.
The plan and design workflow consists of the following:
• Assess your organization’s business requirements to determine recovery requirements.
• Measure your host application’s write-workload in MB per second and write-input/output per
second (IOPS) to begin matching actual data loads with the planned Cnt Ac-J system.
• Use collected data along with your organization’s recovery point objective (RPO) to size Cnt
Ac-J journal volumes. Journal volumes must have enough capacity to hold accumulating data
over extended periods.
The sizing of journal volumes can be influenced by the amount of bandwidth you settle on.
Both efforts are interrelated. You may actually adjust journal volume size in conjunction with
bandwidth to fit the organization’s needs.
• Use IOPS to determine data transfer speed into and out of the journal volumes. Data transfer
speed is determined by the number of Fibre-Channel ports you assign to Cnt Ac-J, and by
RAID group configuration. You need to know port transfer capacity and the number of ports
that your workload data will require.
• Use collected workload data to size bandwidth for the fibre-channel data path. As mentioned,
bandwidth and journal volume sizing, along with data transfer speed, are interrelated.
Bandwidth may be adjusted with the journal volume capacity and data transfer speed you
plan to implement.
• Design the data path network configuration, based on supported configurations, fibre-channel
switches, and the number of ports your data transfer requires.
• Plan data volumes (primary and secondary volumes), based on the sizing of P-VOL and S-VOL,
RAID group considerations, and so on.
• Understand operating system requirements for data and journal volumes.
• Adjust cache memory capacity for Cnt Ac-J.
Some tasks will be handled by HP’ personnel. The planning information you need to address is
provided in the following topics.
Assessing business requirements for data recovery
In a Cnt Ac-J system, when the data path continues to transfer changed data to the remote site,
journals remain fairly empty. However, if a path failure or a prolonged spike in write-data that is
greater than bandwidth occurs, data flow stops. Changed data that is no longer moving to the
secondary system builds up in the master journal.
Plan and design workflow 19