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

Increasing the size of the write history log file in enhanced or basic asynchronous mode
You can expand the size of a DR group member (virtual disk) whether the DR group is in synchronous
or asynchronous mode. However, when you expand the size of a virtual disk in a DR group
operating in enhanced asynchronous or basic asynchronous mode, the write history log file size
does not increase. See the HP P6000 Enterprise Virtual Array Compatibility Reference.
To increase the log file size in enhanced asynchronous mode, you must first set the DR group to
synchronous mode as follows:
NOTE: The following procedure requires you to temporarily change the write mode of the DR
group to synchronous. While host I/O is being replicated synchronously, server performance will
be negatively impacted.
1. Change the write mode from asynchronous to synchronous.
2. Allow the write history log to drain.
3. Increase the size of the log.
4. Change the write mode back to asynchronous.
DR groups with FATA or SAS Midline drives
HP P6000 Continuous Access supports the use of FATA or SAS Midline drives on an array. However,
you must ensure that I/O activity to the source array DR group members does not exceed the
reduced duty cycle requirements for FATA or SAS Midline drives.
Before using FATA or SAS Midline drives in an HP P6000 Continuous Access environment, consider
the following factors:
• FATA drive duty cycle—FATA or SAS Midline drives have a significantly reduced duty cycle
relative to Fibre Channel drives.
• Write I/O rate on the source array— Evaluate the level of write activity to the DR group.
• Type of write I/Os (sequential or random)—Evaluate the type of write I/O to the DR group.
When using FATA or SAS Midline drives on the destination array, you must ensure that the drive
duty cycle will not be exceeded if a DR group failover occurs. In the event of a failover, write and
read I/O is directed to the new source (previously the destination) DR group members. If the read
and write rates and types of writes to the source array do not meet the reduced duty cycle
requirements of the FATA drives, the drives should not be used for DR group destination virtual
disks.
IMPORTANT:
• If your environment requires higher performance and reliability, you may want to consider
using Fibre Channel drives rather than FATA drives for the destination array DR group. This
will ensure a consistent level of operation in the event of a failover.
• When using FATA drives, make sure they have the latest drive firmware installed.
Planning the data replication protocol
Fibre Channel switches typically offer two types of frame routing between nPorts:
• Source ID/Destination ID (SID/DID) routing—Routes all exchanges between a port pair through
the fabric using the same path through the fabric.
• Exchange-based routing—Transfers all frames within a SCSI exchange using the same path.
Other SCSI exchanges can use alternate paths.
38 Planning the array configuration