Storage Virtualization 1

Module 3 Advanced Storage Technology : STORAGE VIRTUALIZATION 1. Virtualization in I/O path 2. Limitations and requirements 3. Definition of Storage Virtualization 4. Storage virtualization on Block and File level 5. Storage virtualization on various levels of Storage network 6. Symmetric and Asymmetric Virtualization

BE IT -A by Shital H. More VIRTUALIZATION

• It is technique of abstracting physical resources. • It simplifies resource management by maximum resource sharing and make them appear as logical resources.

BE IT -A by Shital H. More STORAGE VIRTUALIZATION

Figure 5.1 Storage virtualisation in the storage network moves virtualisation functions from servers and storage devices into the storage network.

This creates a new virtualisation entity which, as a result of its central position in the storage network, spans all servers and storage systems and can thus centrally manage all available storage resources.

BE IT -A by Shital H. More 1. VIRTUALISATION IN THE I/O PATH • Virtualisation is the name given to functions, such as RAID(Redundant Array of Independent Disk), caching, instant copies and remote mirroring.

• Objectives: 1. Increased use of hardware resources 2. Reduced management and resource costs. 3. Improved business flexibility 4. Improved security and reduced downtime.

BE IT -A by Shital H. More 2. LIMITATIONS AND REQUIREMENTS a. Architecture-related limitations of non- virtualised storage networks b. Implementation-related limitations of storage networks c. Proposed Solution :Storage Virtualisation

BE IT -A by Shital H. More a. Architecture-related limitations of non- virtualised storage networks 1. Resource management becomes easier and more flexible. 2. Without storage virtualisation in the storage network there remains a direct connection between the storage devices that provide the storage and the servers that use it. 3. The replacement of storage devices in the event of a defect or an upgrade to newer, more powerful devices give rise to additional costs.

BE IT -A by Shital H. More 4. Without storage virtualisation, every change to the storage resources requires changes to the operating system and to the applications on the servers that use this. 5. There is an inefficient use of the storage resources because no suitable mechanisms have been implemented in the disk subsystems for the sharing of block-level resources.(Fig.1)

BE IT -A by Shital H. More Figure. 1: The storage space on server A is full.

It cannot utilise the free storage space which is available on the volumes for server B.

BE IT -A by Shital H. More b. Implementation-related limitations of storage networks

1. Incompatibilities between the storage systems of different manufacturers.(Fig.2).

2. The lack of standardisation of the interfaces for the disk subsystem-based remote mirroring.

BE IT -A by Shital H. More Figure.2 The incompatibilities that exist between the device drivers for different disk subsystems mean that a server can only use the storage capacity of the corresponding disk subsystems.

BE IT -A by Shital H. More C. Proposed solution: storage virtualisation

• The implementation of a storage network alone does not meet the requirements for the management of large quantities of data. • This requires additional mechanisms that simplify administration and at the same time make it possible to make full use of the storage resources. • The use of storage virtualisation software offers the appropriate possibilities for simplifying the administration of data and storage resources and, on the other, making their use by the users easier.

BE IT -A by Shital H. More C. Proposed solution: storage virtualisation

• The objectives of storage virtualisation : 1. Simplification of the administration and access of storage resources. 2. Full utilisation of the possibilities of a storage network. 3. Realisation of advanced storage functions: – Storage functions such as data backups and archiving, data migration, data integrity, access controls and data sharing should be oriented towards data profiles and run automatically

BE IT -A by Shital H. More 3. Definition of Storage Virtualization • The term ‘storage virtualisation’ is generally used to mean the separation of the storage into the physical implementation level of the storage devices and the logical representation level of the storage for use by operating systems, applications and users. • Storage virtualisation inserts an additional layer between storage devices and storage users (Figure.3) • This forms the interface between virtual and physical storage, by mapping the physical storage onto the virtual and conversely the virtual storage onto the physical

BE IT -A by Shital H. More Figure.3: In storage virtualisation an additional layer is inserted between the storage devices and servers.

This forms the interface between virtual and physical storage

BE IT -A by Shital H. More Module 3 Advanced Storage Technology : STORAGE VIRTUALIZATION 1. Virtualization in I/O path 2. Limitations and requirements 3. Definition of Storage Virtualization 4. Storage virtualization on Block and File level 5. Storage virtualization on various levels of Storage network 6. Symmetric and Asymmetric Virtualization

BE IT -A by Shital H. More 4. Storage virtualization on Block and File level

• Two basic types of virtualisation: a. Virtualisation on block level and b. Virtualisation on file level.

BE IT -A by Shital H. More a. Virtualisation on block level

• Storage capacity is made available to the operating system or the applications in the form of virtual disks (Figure.4).

• The task of the virtualisation entity is to map these virtual blocks to the physical blocks of the storage devices.

BE IT -A by Shital H. More Figure.4: In virtualisation on block level the virtualisation entity provides the virtual storage to the servers in the form of a virtual disk.

BE IT -A by Shital H. More b. Virtualisation on file level

• The virtualisation entity provides virtual storage to the operating systems or applications in the form of files and directories (Figure.5).

• The management of the file system is shifted from the server to the virtualisation entity.

BE IT -A by Shital H. More Figure.5: In virtualisation on file level the virtualisation entity provides the virtual storage to the servers in the form of files and directories.

BE IT -A by Shital H. More Block Level Virtualisation vs. File Level Virtualisation

Block Level Virtualisation File Level Virtualisation 1. Access to virtual 1. Access to virtual storage storage takes place by takes place by means of means of blocks. files or directories. 2. Task of file system 2. Task of file system management is management is performed responsibility of OS or by virtualisation entity. the application. 3. Example : Database 3. Example: NTFS file system in windows 2000 & NT

BE IT -A by Shital H. More 5. Storage virtualization on various levels of Storage network • Depending on the locations at which a Virtualisation entity can be positioned in the storage network, it is classified into the following three levels: 1. Server 2. Storage Devices 3. Network

BE IT -A by Shital H. More Figure.6: A virtualisation entity can be positioned on various levels of the storage network.

BE IT -A by Shital H. More 5.1. Storage virtualisation in the Server

• It is the combination of file system and volume manager. • A volume manager separate the storage into logical view and physical implementation by encapsulating the physical hard disk into logical disk groups and logical volumes. • These are then made available to the applications via file systems.

BE IT -A by Shital H. More The benefits of virtualisation on server level are:

• Tried and tested virtualisation techniques are generally used. • The virtualisation functions can integrate multiple storage systems. • No additional hardware is required in the storage network to perform the virtualisation.

BE IT -A by Shital H. More The disadvantages of virtualisation on server level are:

• The administration of the storage virtualisation must take place on every single server. • Incompatibilities may occur between the virtualisation software and certain applications. • The virtualisation extends only to those areas of a storage network that are accessible or assigned to those servers running a virtualisation entity. • The virtualisation only ever takes place on individual servers.

BE IT -A by Shital H. More 5.2. Storage virtualisation in Storage Devices

• Virtualisation on block level in storage devices is, for example, found in intelligent disk subsystems. • These storage systems make their storage available to several servers via various I/O channels by means of LUN masking and RAID. • The physical hard disks are brought together by the storage devices to form virtual disks, which the servers access using protocols such as SCSI, Fibre Channel FCP, FCoE and iSCSI.

BE IT -A by Shital H. More • Virtualisation on file level in storage devices is, for example, achieved by NAS servers. • The file system management is the responsibility of the NAS server. • Access by the server to the storage resources takes place on file level by means of protocols such as NFS and CIFS.

BE IT -A by Shital H. More The advantages of virtualisation on storage device level are:

• The majority of the administration takes place directly upon the storage device, which is easier and more reliable since it takes place very close to the physical devices. • Advanced storage functions such as RAID and instant copies are realised directly at the physical storage resources, meaning that servers and I/O buses are not loaded.

BE IT -A by Shital H. More The advantages of virtualisation on storage device level are:

• The servers are not placed under additional load by virtualisation operations.

BE IT -A by Shital H. More The disadvantages of virtualisation on storage device level are: • Configuration and implementation of virtualisation are manufacturer-specific and may thus become a proprietary solution in the event of certain incompatibilities with other storage devices. • It is very difficult – and sometimes even impossible – to get storage devices from different manufacturers to work together. • Virtualisation takes place only within a storage system and cannot effectively be expanded to include several such storage devices without additional server software. BE IT -A by Shital H. More 5.3. Storage virtualisation in the Network

• Storage virtualisation by a virtualisation entity in the storage network is realised by symmetric or asymmetric storage virtualisation. • The advantages of virtualisation in the storage network are: 1. The virtualisation can extend over the storage devices of various manufacturers. 2. The virtualisation is available to servers with different operating systems that are connected to the storage network.

BE IT -A by Shital H. More 3. Advanced storage functions, such as mirroring or snapshots can be used on storage devices that do not themselves support these techniques. 4. The administration of storage virtualisation can be performed from a central point. 5. The virtualisation operations load neither the server nor the storage device.

BE IT -A by Shital H. More • The disadvantages are: 1. Additional hardware and software are required in the storage network. 2. A virtualisation entity in the storage network can become a performance bottleneck.

BE IT -A by Shital H. More 6. SYMMETRIC AND ASYMMETRIC STORAGE VIRTUALISATION IN THE NETWORK

• Virtualisation entity is placed in storage network in form of specialised server or device. • Virtualisation entity is called metadata controller. • Management of storage resources and control of all storage functions.

BE IT -A by Shital H. More 6. SYMMETRIC AND ASYMMETRIC STORAGE VIRTUALISATION IN THE NETWORK • Symmetric and asymmetric virtualisation differ primarily with regard to their distribution of data and control flow. • Data Flow : Application Data • Control Flow : all metadata and control information • In symmetric storage virtualisation the data flow & the control flow travel down the same path. • In asymmetric virtualisation the data flow is separated from the control flow.

BE IT -A by Shital H. More 6.1. Symmetric Storage virtualisation

• The data and control flow is done on the same path (Figure.7).

• Symmetric virtualisation is also called In-band virtualisation.

BE IT -A by Shital H. More Figure.7: In symmetric virtualisation, data and control flow travel down the same path.

BE IT -A by Shital H. More 6.1. Symmetric Storage virtualisation

• Virtualisation is logically structured in two layers (Figure.8): – The volume manager layer – The data access layer • The volume management layer is responsible for the management and configuration of the storage devices that can be accessed directly or via a storage network.

BE IT -A by Shital H. More Figure.8: In symmetric virtualisation the metadata controller consists of a data access layer and a volume management layer

BE IT -A by Shital H. More • The data access layer makes the logical drives available for access either on block or file level, depending upon what degree of abstraction is required. These logical drives can thus be made available to the application servers by means of appropriate protocols. • In the case of virtualisation on block level, this occurs in the form of a virtual disk and in the case of virtualisation on file level it takes place in the form of a file system.

BE IT -A by Shital H. More • The advantages of symmetric virtualisation are evident: 1. The application servers can easily be provided with data access both on block and file level, regardless of the underlying physical storage devices.

2. The administrator has complete control over which storage resources are available to which servers at a central point. This increases security and eases the administration.

BE IT -A by Shital H. More • The advantages of symmetric virtualisation are evident: 3. The performance of existing storage networks can be improved by the use of caching and clustering in the metadata controllers.

4. Assuming that the appropriate protocols are supported, symmetric virtualisation does not place any limit on specific operating system platforms. It can thus also be used in heterogeneous environments.

BE IT -A by Shital H. More • The disadvantages of symmetric virtualisation are evident: 1. Each individual metadata controller must be administered.

2. It can sometimes be difficult to move the data between storage devices if this is managed by different metadata controllers

BE IT -A by Shital H. More 6.2. Asymmetric Storage virtualisation

• The data flow is separated from the control flow. (Figure .9).

• This approach is also called out-band virtualisation.

BE IT -A by Shital H. More Figure.9: In asymmetric virtualisation the data flow is separated from the control flow. BE IT -A by Shital H. More • The metadata controller is logically structured in two layers (Figure.10). 1. The volume management layer has the same duties as in the symmetric approach. 2. The second layer is the control layer, which is responsible for the communication with an agent software that runs on the servers.

BE IT -A by Shital H. More Figure.10: In asymmetric virtualisation the metadata controller takes on only the administrative control tasks for the virtualisation. Access to the physical storage is realisedBE ITby -A means by Shital H. ofMore an agent software. The advantages of asymmetric virtualisation are : • Complete control of storage resources by an absolutely centralised management on the metadata controller. • Maximum throughput between servers and storage devices by the separation of the control flow from the data flow, thus avoiding additional devices in the data path. • To improve fault-tolerance, several metadata controllers can be brought together to form a cluster.

BE IT -A by Shital H. More The Disadvantages of asymmetric virtualisation are: • A special agent software is required on the servers or the host bus adapters. So there is Incompatibilities exist between the agent software and existing applications. • The agent software must be absolutely stable in order to avoid errors in storage accesses. In situations where there are many different platforms to be supported, this is a very complex development and testing task . • The development cost increases further if the agent software and the metadata controller are also to permit access on file level in addition to access on block level. BE IT -A by Shital H. More The Disadvantages of asymmetric virtualisation are: • A performance bottleneck can arise as a result of the frequent communication between agent software and metadata controller. • In asymmetric virtualisation there is always the risk of a server with no agent software being connected to the storage network.

BE IT -A by Shital H. More