VMware's vCenter Server 5 Essentials Pack, a commonly used virtualization platform, has an optional software plug-in or add-on known as VSA (vSphere Storage Appliance). The main function performed by the VSA add-on is to create a shared storage pool and replicate data between internal components of the pool as needed to create high data availability. The concept used by the VSA system is well understood in the industry, and has been embodied in non-VMware products such as LeftHand (produced by HP).
In the case of VMware's VSA, however, users should be aware that it currently has some limitations. These limitations are fully disclosed in the VSA documentation supplied by VMware. For example, VSA's design means that it has limitations in terms of scalability; the current version of the product can scale to two or three storage nodes, but not beyond. In addition, it will only be able to scale to the number of nodes with which a user began. Another limitation is that each VSA cluster can support eight disks at most in a storage cluster. IT services personnel will need to be careful during the installation process because VSA 1.0 does not allow storage to be added after clusters have been configured.
While these limitations may be a cause for concern, the rationale behind them is sound. Limits on capacity can mean that the availability of data is increased. This is an important issue for small and medium sized businesses whose business model places data at the heart of their operations.