Development status and future trend of virtualization storage technology (II.)

③ Virtualization based on routers

The router based approach is to implement storage virtualization on the router firmware. Vendors often also provide additional software to run on the host to further enhance storage management capabilities. In this method, the router is placed in a data channel on each host to the storage network to intercept any command from the host to the storage system in the network. Because routers potentially serve each host, most control modules exist in the firmware of the router, which is better and more effective than the host-based and most interconnected devices based methods. This method has better security than host-based or device based methods because it is not dependent on a proxy server running on each host. When a router connecting a host to a storage network fails, it can still cause data on the host to be inaccessible. However, only hosts that are connected to the failed router are affected, and other hosts can still access the storage system through other routers. The redundancy of routers can support dynamic multipath, which provides a solution to the above fault problem. Because routers are often used as a bridge for protocol conversion, a router based approach can also provide interoperability between heterogeneous operating systems and multi-vendor storage environments.

Third, the development foreground of the virtual storage technology

① Each method has its advantages and disadvantages

Host-based and storage based methods are most attractive to early-stage users because they do not require any additional hardware, but the system does not work well for heterogeneous storage systems and operating systems. A switch based or router based approach may be more appropriate for businesses that require maximum interoperability. For those who require higher scalability, the router based approach is the optimal choice. The method based on interconnect devices is between the two, it avoids some security problems, the storage virtualization has a strong function, can reduce the load of single host, and can get good extensibility.

Different vendors have different storage virtualization implementations, some are biased towards replication, some are good at backup, while others have better performance in recovery and access control. Storage management software vendors tend to provide the most complete set of management packages. However, multi-platform support and optimal performance characteristics are not easy to achieve.

Several mirroring methods have been developed in the area of data replication. Many storage vendors provide a three-tier mirror structure, and VERITAS companies can even provide four-tier mirroring structures. Mirroring is respected in some respects, and full mirroring can produce identical copies on another drive. This additional copy is sometimes referred to as a snapshot, which stores only previous versions of the data. Sometimes, a replica drive that exists in a different geographical location can generate remote or asynchronous replicas via IP.

In a storage network, storage access control is often performed in partitioned (zoning)-type hosts and storage systems. Only hosts belonging to the same partition can access the storage device for this partition. Hosts and storage devices are often a member of multiple partitions. The idea of zoning is similar to a virtual private storage network.

There are several ways to partition. As the granularity and management of shared storage are different, partitioning methods vary widely. Port-based partitions are often implemented in the switch, and access within the switch must take place between the specified ports. This zoning is characterized by the inability to overlap between partitions. partitions need to be reconfigured when the specified port partition member is changed. This approach has obvious drawbacks because, in most cases, changing the consistency of partition members is not allowed even if the switch port is tuned.

subsystem partitions or volume mappings are often implemented by the controller of the internal disk subsystem, which allows the entire or partial drive to become its data outlet, making the single storage subsystem look like multiple drives and multiple hosts. Partitions based on the logical unit device number Mask (LUN masking) are implemented on the host I/O controller, host software, or router. The LUN mask, like a filter, allows only the host to access specific storage resources, and it also allows a single drive in one storage subsystem to belong to a different partition, resulting in a device-level partition.

② Network Virtual Most Promising

From the perspective of development trends, host-based and storage based virtualization technology is now relatively mature, users can fully enjoy the benefits of it, and because they have entered a mature period, so the price is low. In both respects, HP has launched the server layer virtual Replicator, storage layer of StorageWorks EVA and Va. And the network virtualization is a new technology, it is independent of the host and storage devices, so that users have a lot of flexibility, the future development of the largest space. April 2003, Hewlett-Packard launched the Storageapps sv3000 and other virtualization products, currently has hundreds of users in the use of this technology, believe that it brings users the greatest benefits. Although network virtualization is an emerging area, it has a lot of room to grow, and even the realization of this virtualization on the web is called a second-generation San or next-generation SAN.