Storage virtualization

Storage virtualization is changing a technique from computer science to the physical characteristics of available memory over users apparently. The technique is used, so that users do not have to necessarily along the physical boundaries, such as per hard drive or memory per unit, divide the available space. Through storage virtualization users space appears, therefore, virtually: The space may well be divided into storage systems or hard drives, only those media do not have to be physically present. A software ensures that the virtual memory allocation fits on a suitable manner to the physically available memory.

Users will benefit from storage virtualization, by not being tied to physical limitations. Restructure or expand the physical memory range disturbs users of the bid less memory when the memory virtualized available. For Managers of advantage on the other hand is that the existing physical memory range can be effectively divided between the existing users. The utilization rate improved.

There are several technological approaches to storage virtualization to perform

Virtualization method: Out of Band or switch -based

The consideration of the out of band storage virtualization is only academically necessary today. The products that have followed these approaches have been forced out of the market. This is due, above all, the very complex setup that was necessary for this type of storage virtualization.

This approach promises that the actual virtualization systems are located outside of the data path. The actual virtualization is performed in switch systems. Here there is the logical combination of disk areas to virtual drives.

Advantages:

  • No obstruction in the data path. As the virtualization performs very close to the switch, one talks of IO delays by about 30 microseconds per IO. This is comparatively little, if one assumes that a disk access takes place in the millisecond range.

Cons:

  • No way to establish caching in the data path. Thus, the power of virtualization on the individual performance and therefore also the cost of the underlying storage systems depends.

Examples: EMC Invista, LSI SVM and HP SSPA

Method of virtualization: Virtualization on a storage system

Virtualization is directly in a memory system performed which now has the ability to integrate third-party memory into its own processing.

Advantages:

  • A storage system that can be individually extended with external memory. All functions can now be managed from a central location.
  • The concept is well suited to the consolidation of various storage systems.

Cons:

  • Due to the high value of consolidation, there is the danger that it is much cheaper, even expand the memory system to connect as secondary storage to the system. This again contradicts the virtualization approach especially when the storage virtualization is considered as a future concept.

Example: HDS USP -V, HP P9000 XP, IBM Storwize V7000 and OEM derivatives SUN

Virtualization Method: In Volume

Special virtualization systems are established in the SAN in the data path. Each IO is passed through these systems and mapped according to the disk blocks.

Advantages:

  • Virtualization is completely transparent to the server.
  • The virtualization system is used to store instance: the servers do not require special drivers for the storage hardware, as they can no longer see them.
  • By integrated cache, the performance of the system can be improved.
  • Cheaper storage systems can thus provide much higher performance.

Cons:

  • Whenever the virtualization system has weak characteristics cache memory performance is deteriorated.
  • Increased latency through the use of a layer is generally compensated for by the cache.

Examples: FalconStor IPStor, IBM San Volume Controller SVC, DataCore SANsymphony - V Storage Hypervisor

Virtualization Method: Host-based

A driver on the host system does all the virtualization features.

Advantages:

  • There is no need for additional hardware.
  • Best performance of all storage virtualization method, since all storage devices always directly, ie (in band cf ) and thus can be addressed without additional latencies without intermediate instances. Caching process on the host allow additional accelerations and are inherently faster than caches in the SAN.
  • Any scalable, the limiting factor is primarily the number of possible I / O controller.
  • Easy access to the functions of the storage virtualization by the host operating system or even from within applications.
  • This particular suitability for use with virtual machines.
  • Easy replacement of the storage systems, host-controlled live migration of data between storage systems.

Cons:

  • The host-based storage virtualization must be ported to any desired platform and is therefore usually only available for selected operating systems.
  • In the SAN may have multiple host simultaneously access the storage resources. Only a cluster-enabled host-based storage virtualization can solve the resulting problems, but then offers more convenience, for example, for high -availability solutions, live migrations and resource sharing.

Examples: Veritas / Symantec Storage Foundation, OSL Storage Cluster, Linux Logical Volume Manager

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