Sharing is done via iSCSI across the network that connects to two physical hosts. Additional virtual hosts would have access to this shared storage by that iSCSI interconnection. Assuming there is excess capacity, this allows the virtual environment to quickly see how shared storage can benefit them without needing to purchase additional servers or storage. Most environments will move to a stand alone set of systems to serve up storage, although some work just fine in this configuration. Since there is no change to the software, migration from the virtual version to a standalone version it relatively straight forward.
HP's LeftHand Networks is known for its clustered approach to storage, so bringing that concept to the virtual environment seems natural. Similar to DataCore, HP uses the same software in the virtual environment as it does in the stand alone environment, unlike the DataCore solution, the HP solution clusters storage across all the available server hosts in the virtual cluster. In this implementation a virtual machine is created on each physical host. Each virtual machine is assigned a specific amount of capacity, ideally the size of that capacity is consistent, and that capacity is then pooled into one logical partition. Then as regular virtual machines are created they are assigned capacity from that pool and data is striped across the virtual machines.
Similar to the DataCore example this is most often used to evaluate the LeftHand's storage software, but a growing number of users are using it as a production storage solution. HP also provides a product called Cluster Swap that can move the data from the virtual servers to a stand alone storage configuration.
While both of these solutions are most commonly deployed in evaluation scenarios, as the processing capabilities of the virtual hosts becomes more and more powerful there will be continued excess processing capacity. Why not use that capacity to manage the storage requirements of environments with modest storage I/O demands? With each iteration of the Intel processor, that performance capability will continue to increase and tempt more users to this type of solution.
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George Crump is lead analyst of Storage Switzerland, an IT analyst firm focused on the storage and virtualization segments. Find Storage Switzerland's disclosure statement here.