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

Planning DR groups
Virtual disks that contain the data for one application must be in one DR group. For optimum
failover performance, limit the virtual disks in a DR group to as few as possible.
DR group guidelines
The following guidelines apply for DR groups:
• Source and destination arrays must have remote replication licenses.
• The maximum number of virtual disks in a DR group and the maximum number of DR groups
per array vary with controller software versions. For current supported limits, see the HP P6000
Enterprise Virtual Array Compatibility Reference.
• The array selected as the destination is specified by the administrator when setting up replication
and creating the DR group.
• All virtual disks that contain data for a common application must be in a common DR group.
HP recommends one application per DR group.
• All interdependent virtual disks such as host based logical volumes must be in a common DR
group.
• DR groups can contain members from multiple disk groups.
• DR group members can exist in any supported redundancy (Vraid) level.
• DR groups that include FATA drives must meet the necessary configuration requirements. For
more information on FATA drives, see “DR groups with FATA or SAS Midline drives” (page 38).
• All members of a DR group have a common preferred controller. Virtual disks added to a DR
group will take on the presentation and failover status of the first virtual disk that was added
to the disk group. The preferred mode setting is failover/failback.
• With some versions of controller software, virtual disks cannot be added to or deleted from
a DR group when operating in enhanced asynchronous or basic asynchronous write mode.
You must change the DR group to synchronous write mode and wait for the write history log
or the write pending queue to drain before you can add or remove members. This restriction
is controller software version dependent. To determine if your array has this restriction, see
the HP P6000 Enterprise Virtual Array Compatibility Reference.
• Failover is permitted only from the destination array.
• When failsafe mode is enabled, a DR group cannot be suspended.
• A suspended DR group cannot be failed over and its members cannot be removed. Exception:
if ISLs are broken, a suspended DR group can be failed over.
• A DR group cannot be deleted if a member of the DR group is presented on the destination
array.
• LUN shrink of virtual disks in a DR group is not supported for any VCS or XCS controller
software versions. See the HP P6000 Enterprise Virtual Array Compatibility Reference to
determine if your array supports this feature. LUN expansion is not supported on VCS 3.xxx.
• A DR group can be failed over or deleted while it is normalizing in controller software version
0952x000 or later.
• Some versions of controller software support auto suspend when a full copy of the DR group
is required. This feature can be used to protect the data at the destination site by delaying the
full copy operation until a snapshot or snapclone of the data has been made. See the HP
P6000 Enterprise Virtual Array Compatibility Reference to determine if your array supports
this feature.
36 Planning the array configuration