HP P6000 Continuous Access Implementation Guide (T3680-96431, August 2012)

4 Planning the array configuration
This chapter provides an overview of factors to consider when planning an array configuration for
remote replication.
Many remote replication features depend on the array controller software. For more information
about planning, see the HP Enterprise Virtual Array Configuration Best Practices White Paper for
your array model.
Planning disk groups
Planning the necessary disk groups to meet your I/O requirements should be done when configuring
the array. See the HP Enterprise Virtual Array Configuration Best Practices White Paper for
recommendations on configuring the array properly.
When data is replicated remotely, application performance is not necessarily improved by increasing
the number of disks in a disk group because response time for application writes includes the time
for replication. In addition, sequential access (read or write) is limited by the per-disk performance
rather than by the number of disks in the disk group. In synchronous mode, performance will likely
be limited by replication before it is limited by the number of disks. When using enhanced
asynchronous write mode, DR group logging will impact the write workload imposed on the array.
Determining the number of disk groups
To determine if the default disk group will meet your remote replication needs, consider the following:
• Separate disk groups can help ensure that data is recoverable if a disk group fails. However,
multiple disk groups result in a slightly higher cost of ownership and potentially lower
performance.
• In general, distributing the workload across the greatest number of disks in a single disk group
provides the best performance.
• Disk groups must provide sufficient free space for snapshots and snapclones (if used), and for
DR group write history logs.
• A DR group can contain virtual disks from multiple disk groups, but all DR group member
virtual disks must be in the same array and must be set to use the same preferred controller
on the array.
For specific guidelines on choosing the number and size of disk groups, see the HP Enterprise
Virtual Array Configuration Best Practices White Paper for your array model.
Specifying disk group properties
Use HP P6000 Command View to initialize each local and remote array and create additional
disk groups as needed. When configuring disk groups for remote replication, consider the following:
• Assign different names to local and remote arrays to ensure the ability to fail over DR groups.
• Select disk protection level double for disk groups that will contain DR group members. (Note
that this differs from the best practice in nonreplicating configurations.) The protection level
determines the capacity reserved for reconstructing disks after a disk failure. Selecting double
disk protection reserves the largest amount of disk capacity and provides the most data
protection.
• Calculate the disk group occupancy alarm setting according to the array best practice, and
ensure that you include the total maximum capacity for all DR group write history logs. See
the HP Enterprise Virtual Array Configuration Best Practices White Paper for your array model.
Planning disk groups 35