Cloud Computing: Virtualization Technology (2)--Storage virtualization

Storage Virtualization

As the demand for storage spirals up, the storage servers and arrays within the company multiplied without exception. One solution to this storage-management dilemma is storage virtualization. Storage virtualization enables management programmers to identify, configure, and manage different storage as resources for a single collection. Storage virtualization is an important part of storage consolidation that reduces management problems and improves storage utilization, which lowers the cost of new storage.

The definition given by the authoritative agency s N I A (Storage Network Industry Association)

"Implement storage and data management independent of applications and networks by abstracting, hiding, or isolating storage-system/subsystem internal functions from applications, computing servers, network resources."

Storage virtualization technology is to abstract the underlying storage devices unified management, to the server layer to mask the specificity of storage equipment hardware, but only to retain their unified logic characteristics, so as to achieve a centralized storage system, unified and convenient management.

Comparison with traditional storage

Compared with traditional storage, the advantages of virtualization storage are mainly reflected in: high disk utilization, traditional storage technology, disk utilization is generally only 30-70%, and the use of virtualization technology disk utilization up to 70-90%, storage flexibility, can adapt to different vendors, different types of heterogeneous storage platforms, Provides greater flexibility for storage resource management, easy to manage, provides a centralized management of large capacity storage systems, and avoids the management headaches associated with storage device expansion; better performance, virtualized storage systems for load balancing, The bandwidth required for each data access is reasonably allocated to each enclosure to improve the overall access bandwidth of the system.

Classification

There are a variety of classifications for virtualized storage, ranging from a large aspect to a classification based on the location of virtualization in the I/O path, sorted according to the different control paths and data paths. Depending on where virtualization is implemented in the I/O path, virtualized storage can be divided into virtual storage of hosts, virtual storage of the network, and virtual storage of storage devices. Depending on the control path and data path, virtualized storage is divided into symmetric virtualization and asymmetric virtualization.

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Advantages：

Storage virtualization can also improve usability. If an application is associated with certain storage resources, any disruption to those resources will reduce the usability of the application. With storage virtualization, applications are no longer associated with a physical stored program.

Storage virtualization may help automate storage capacity augmentation. Without the need for manual configuration, storage virtualization can use policies to allocate more storage capacity to the required applications. Storage virtualization can also allow storage resources to be changed or upgraded during delivery without disrupting application performance and reducing the storage downtime required for repair and maintenance.

Shortcomings：

The downside to storage virtualization is the added complexity. The storage layer is a new part of the storage environment and must be managed and maintained as the virtual product is patched and updated. Similarly, interoperability and compatibility between storage devices can also be affected. In some cases, the virtual layer may interfere with certain features of the storage system, such as remote replication. For example, a storage array containing local remote replication, when used in virtualized environments, may not be able to provide this replicated service. Only laboratory tests and evaluation results can reveal this potential problem.

Another problem is the difficulty of recovering or canceling the operation once the storage virtualization is implemented. This is not impossible, but the process of associating the application with the storage location is prone to error. Experts recommend gradual implementation of partial storage virtualization, which is partially deployed in one or several applications before being extended to the data center and the entire company.

Three-layer model

According to the composition and characteristics of cloud storage system, the model of virtualized storage can be divided into three layers: physical device virtualization layer, storage node virtualization layer, storage Area Network virtualization layer. The three-layer virtualization storage model greatly reduces the complexity of storage management, effectively encapsulates the complexity and diversity of the underlying storage devices, and makes the system more scalable and flexible. By adding storage devices to a storage pool and simply configuring them, users can create virtual volumes without having to focus on the physical storage capacity of individual devices in the system and the properties of the storage media to achieve unified storage management.

Physical Device Virtualization Layer:

Mainly used for data block-level resource allocation and management, using the underlying physical device to create a continuous logical address space, that is, storage pool. Depending on the properties of the physical device and the needs of the user, the storage pool can have several different data attributes, such as read and write features, performance weights, and reliability levels. Storage devices on demand, as a logical Volume manager, can allocate logical volumes from storage pools, dynamically allocate storage resources, and manage the mapping and forwarding of data blocks.

Storage Node Virtualization layer:

Enables resource allocation and management between multiple storage pools within a storage node, consolidating one or more allocated storage pools into a unified virtual storage pool within the storage node scope. This virtualization layer is implemented by the Storage node virtual module within the storage node, the storage device that manages on-demand, and on the storage Area Network virtualization layer.

Storage Area Network Virtualization layer:

Enables the allocation and management of resources between storage nodes, and centrally manages storage pools on all storage devices to form a unified virtual storage pool. This virtualization layer is implemented by Virtual Storage Management module on virtual Storage Management Server to manage the resource allocation of virtual storage system in an Out-of-band virtualization way, providing address mapping, querying and other services for virtual Disk Management.