Storage Virtualization and vendor lock in
by Hu Yoshida on Feb 3, 2007
Experts agree that virtualization has the potential to simplify storage administration, increase utilization and availability, and reduce the cost of managing different vendor’s storage products by masking the differentiation that vendors strive to create to capture market share. Essentially the expert’s goal is to commoditize storage so that it is just a matter of choosing the largest capacity for the lowest price. Sounds simple doesn’t it?
Unfortunately the value of storage is not just about capacity. The real value of storage is in providing storage and data services to host applications. Services which are used to protect data, storing it at the right cost level, replicating data for use by other applications, making it available to authorized users, with the required level of cost performance, monitoring and reporting on the use of this data for charge back and auditing. As data volumes and transaction rates increase, the storage must scale in capacity, connectivity, and bandwidth. Storage services must be available to migrate the data to new storage when the old storage wears out, becomes technologically obsolete, becomes uneconomical, or is acquired or transferred to another owner. In a networked, shared environment, storage services must also be available to ensure that data is protected from unauthorized access, or denial of service. All this and more must be done with minimal disruption to the applications using the data. These storage and data services are provided by the storage controller.
SAN based virtualization appliances are mainly focused on the aggregation of storage systems and not the virtualization of storage services. These storage services are complex functions which require multiprocessor architectures with access to a large global cache, the type of specialized architecture that is found in Enterprise Storage controllers. There are no common set of services, no common denominator, for all the vendors to use since these functions are dependent on the architecture of each vendors storage controller.
In fact I don’t believe that customers want all storage vendors to do these services in the same manner. I believe customers want vendors to compete and continuously improve and add services in order to meet changing business requirements.
Hitachi has implemented storage virtualization in the storage controller to provide all the cutting edge storage services that has been developed over the years to externally attached storage. This approach not only provides aggregation of storage systems, it also provides virtualization of storage services.
Some experts criticize this approach as being a vendor lock in. I contend that storage virtualization that is done in storage control unit does not create a vendor lock in. Unlike other virtualization approaches that require the use of mapping tables to map storage extents into mdisks (managed disks) and then map mdisks to vdisk (virtual disks) for presentation to the host server, the storage controller approach does not require a mapping table.
Storage controller virtualization discovers the LUNs on the external storage through standard FC SCSI commands. After the LUNs are discovered, they are presented through the storage controller cache as though they were internal LUNs. The mapping of the LUN extents is done in the external storage and stays with the external storage system. If you don’t like the services that the Hitachi storage controller provides, you can disconnect and go back to native use or connect to other storage virtualization products or storage controllers. This is not a vendor lockin. Any storage virtualization approach that requires a mapping table is a vendor lock in. It requires you to use that vendor’s mapping table.
Storage virtualization must do more than aggregate storage systems. Storage virtualization must also virtualize storage and data services so that applications can use a common set of storage services and administrators can use a comon set of tools. Storage virtualization can only be done in a storage controller. Currently Hitachi is the only vendor to provide this. I believe that other vendors will follow suit. Watch what start ups like Pillar and 3PAR Data are doing. The only difference is that Hitachi does not limit the attachment of external storage to Hitachi storage.