HP P6000 Replication Solutions Manager User Guide (T3680-96089, October 2012)

Controller software features
The properties of storage systems, their virtual disks, and replication features depend upon the
controller software version. For information about controller software versions that are supported
with HP P6000 Replication Solutions Manager, see Table 1.0,HP P6000 software solutions
compatibility, in the HP P6000 Enterprise Virtual Array Compatibility Reference. See (page 288).for
document location.
For support, visit the HP Storage website. See (page 289).
Controller software features - local replication
HP P6000 Replication Solutions Manager supports the local replication features of the HP P6000
EVA controller software. For more information, see Table 6.2, Supported local replication features
by controller software version, in the HP P6000 Enterprise Virtual Array Compatibility Reference.
See (page 288) for document location. For support of newer versions, visit the HP Storage website.
Controller software features - remote replication
HP P6000 Replication Solutions Manager supports the remote replication features of the HP P6000
EVA controller software listed below. For more information, see Table 6.3, Supported remote
replication features by controller software version, in the HP P6000 Enterprise Virtual Array
Compatibility Reference. See (page 288) for document location. For support of newer versions, visit
the HP Storage website.
Cache policies
Each virtual disk on a storage system has a read cache and a write cache. The following are key
cache policies (settings): Write cache, Write cache mirror, and Read cache.
Write cache
The virtual disk write cache policy specifies how host writes to virtual disks are performed. Values
are:
• Write-back. The storage system notifies a host that a write operation is complete after data is
written to the storage system cache memory (but before the data is written from the cache to
disk media). Write-back is the default.
• Write-through. The storage system notifies a host that a write operation is complete after the
data is written from the cache to disk media.
Write-back caching improves host write performance because data is written to the high speed
cache memory faster then to disk media. Write-through caching is safer, in terms of fault tolerance.
Storage systems that are fully functional use write-back only. Under certain failure conditions,
storage systems automatically switch to write-through for data safety.
Actual and requested values. Policy values are reported as actual and requested. An actual value
is the policy that is in effect for the virtual disk. A requested value is a value that has been requested
but is not yet in effect. For example, a policy change can be requested when a virtual disk is not
presented to a host but the change does not take effect until the disk is presented to a host.
Write cache mirror
The virtual disk write cache mirror policy specifies whether each controller in a storage system
contains a copy of the other controller's write cache. The following values are reported:
• Enabled. In the storage system, each controller contains a copy of the other controller's write
cache. Enabled is the default.
• Disabled. In the storage system, the controller does not contain a copy of the companion
controller's write cache.
256 Virtual disks