11.0 HP StoreVirtual Storage User Guide (AX696-96275, December 2013)

10 Working with clusters
Clusters are groups of storage systems created in a management group. Clusters create a pool of
storage from which to create volumes. The volumes seamlessly span the storage systems in the
cluster. Expand the capacity of the storage pool by adding storage systems to the cluster.
Prerequisites
To create a new cluster, you need the following:
• An existing management group
• At least one storage system in the management group that is not already in a cluster
• A designated VIP address for the cluster
VIPs are required for iSCSI load balancing and fault tolerance, and for using HP StoreVirtual DSM
for Microsoft MPIO. For more information, see “HP StoreVirtual Storage using iSCSI and Fibre
Channel” (page 241). Although Fibre Channel connections do not require a VIP, because a cluster
can contain both Fibre Channel and iSCSI volumes, a VIP is always required in the cluster.
Clusters and storage systems
When creating clusters and when adding storage systems to clusters, consider storage system
capacity and the number of storage systems planned.
• Storage system capacity—Typically you create clusters with storage systems of the same
capacity. While clusters can contain storage systems with different capacities, all storage
systems in a cluster operate at a capacity equal to that of the smallest-capacity storage system.
The capacity limitation applies to the available capacity as determined by the disk RAID level,
not the raw disk capacity.
This capacity impact is particularly important to consider when planning to add storage systems
to an existing cluster. If you add a storage system with a smaller capacity, the capacity of the
entire cluster will be reduced. For example, If you have three storage systems, two of which
have a RAID-determined capacity of 1 TB, and one of which has a RAID-determined capacity
of 2 TB, all three storage systems operate at the 1 TB capacity.
NOTE: While it is possible to mix storage systems with different disk RAID levels, it is not
recommended.
• Number of storage systems in clusters—The optimum number of storage systems in a cluster
ranges up to 10. For more information about the recommended maximum number of storage
systems that can be added safely to a cluster, see “Configuration Summary overview”
(page 107).
• Adaptive Optimization in clusters—Adaptive Optimization stores data which is accessed most
frequently on the fastest performing media in a storage system—typically solid state
drives. Adaptive Optimization in HP StoreVirtual automatically adapts to changing workloads
and moves data accordingly and transparently. After Adaptive Optimization is enabled, the
LeftHand OS stores the most accessed data to faster/higher tiers in the Adaptive
Optimization-capable storage tier.
Using Adaptive Optimization requires using storage systems with multiple tiers of storage
(called Adaptive Optimization-capable) in a cluster. When adding an Adaptive
Optimization–capable storage system to a cluster, Adaptive Optimization becomes enabled
for the cluster. The cluster Details tab reports the Adaptive Optimization status of the cluster
in the Cluster section, as well as the used space by tiers in the Disk Usage section. For more
132 Working with clusters