Storage Virtualization

Topics Definition of Storage Virtualization Implementation Considerations Storage Virtualization on Block or File level Storage Virtualization on various levels of the Storage Network

Definition of Storage Virtualization Separation of the storage into the physical implementation level and the logical representation level for use by OS, applications and users. Virtualization: At various levels – Server, Storage and Network. Add an additional layer between storage devices and storage users.

Storage virtualization does 2 things: Physical storage is abstracted to logical storage by aggregating several physical storage units to form one or more logical unit, Virtual Storage Unit. OS and applications do not have direct access to the physical storage devices, they use virtual devices. Mapping from virtual to physical and vice versa is done using virtualization layer. Example: JBOD, volume manager aggregating multiple physical disks to form a large logical volume. Storage virtualization does 2 things: Provide access to OS and applications Map requests from logical disks to physical disks.

Virtualization entities can be used concurrently. It can be implemented as both hardware and software on various levels in a storage network. Virtualization entities can be used concurrently. Virtual volume being used by server Virtual volume exported by disk sub-systems

Implementation Considerations Draw general requirements and considerations for implementation How difficulties can be solved. Realization of the virtualization entity Administration of the entity should be done using central console regardless of hardware or software implementation and its position in the network. All operations performed by the entity should take place in a rule- based manner and orientate to the application data profile. Policy-based operation allows to configure and control the operations of the entity.

Virtualized storage resources should be backed up so that access can be given even in the event of failure. To provide greater degree of compatibility to servers and applications, entity should be hidden from its users. Servers, applications and users should have the impression that they are working with the physical storage and should not notice virtualized entity. Non-virtualized storage access should also be included because many devices (servers) are incompatible with virtualization.

2. Exchange of storage devices Exchange of storage devices is easy when using virtualization because servers do not have direct access to physical storage. Steps involved are: Connection of new storage device to the storage network. Configuration and connection of the new device to the virtualization entity. Migration of data from old device to new device while applications are still running. Removal of old device from configuration of virtualization entity. Removal of old device from the storage network. No changes to the applications and they keep working during this process.

3. Efficient use of resources by dynamic storage allocation All storage resources can be shared. Capacity can be dynamically changed to match changing requirements and growing data needs and freeing resources when need shrinks. More easily done in file level than in block level. File level includes information of free blocks. 4. Efficient use of resources by data migration Based on how often the data is required, entity can distribute data in fast and slow storage devices: high throughput for frequent data. Example: Store the start of video in fast device and rest in slow device.

5. Performance increase Caching to reduce number of slow physical access. Striping and mirroring can be used to increase performance. Distribution of I/O load among different virtualization entities and several paths. 6. Availability due to the introduction of redundancy Redundancy is introduced by the virtualization entity as it has complete control over data. If a storage device fails, mirrored data is copied to restore redundancy. Failure of the device is completely hidden from the servers, apart from performance reduction.

Device failure information must be sent to the central console so that the component is replaced. Multiple access paths between servers and virtual storage and between virtual storage and physical storage to increase fault- tolerance. 7. Back-up and archiving By using proper rules, virtualization entity should take periodic back- ups of data independently. 8. Data sharing Data sharing is possible if file level access is permitted and virtualization entity manages the file system centrally. Permitted in NFS, CIFS. Working on cross-platform shared disk file systems.

9. Privacy Protection User rights and access configurations can be integrated into the virtualization entity. Central management of access rights.

Storage Virtualization on Block or File Level Regardless of where we perform virtualization, it can be divided into 2 types: Virtualization on block level Virtualization on file level Block level means storage is made available to the OS or applications in the form of virtual disks. OS and applications work on the blocks of the virtual disk. These blocks are managed like blocks of physical storage by a file system or a database server.

Virtualization entity should map virtual blocks to physical blocks. Virtualization can be done multiple times. Mapping becomes a bit complex.

Virtualization on file level means that virtualization entity provides virtual storage to the OS and applications in the form of files and directories. Conversion of virtual blocks to files is done by the entity. Physical blocks are presented in the form of virtual file system managed by virtualization entity itself.

Access to virtual storage takes place using blocks. Block level File level Access to virtual storage takes place using blocks. File system management is done by the OS. Suitable in an environment wherein there are different types of OS and applications and they use only block data. Access to virtual storage takes place using files. File system is managed by the virtualization entity. Suitable in an environment wherein data sharing is required and is accomplished using files.

Storage Virtualization on Various Levels of the Storage Network Different levels of virtualization are: Server Storage device Network

Storage virtualization in the server Classic representative of virtualization in the server is the combination of file system and volume manager. Volume manager forms logical volumes and these are made available to the applications using file systems. Some volume managers provide additional services such as RAID, snapshots, dynamic reconfigurations. In shared disk file system, this cannot be used in a straight-forward manner because of the incompatibilities.

Administration in each server and software should be used for this. Disadvantages Advantages Administration in each server and software should be used for this. It can consume resources and degrade server performance. Incompatibilities between virtualization software and applications. Virtualization is limited to storage networks that are assigned to the server. Virtualization takes place in only one server. Clustered servers can be used but additional costs are involved. Tried and tested virtualization techniques are used. Virtualization function can link in several storage systems. No additional hardware is required in the storage network.

Storage virtualization in storage devices Virtualization on block level in storage devices is found within intelligent disk-subsystems. Storage is available to several servers via various I/O channels by means of LUN masking and RAID. Virtualization on file level is achieved in NAS servers, data is accessed in terms of files using NFS and CIFS protocols.

Virtualization operations do not place any additional load on servers. Disadvantages Advantages Easy and more reliable since it takes place very close to physical devices. Advanced functions are realized in physical storage device freeing up the CPU and I/O buses. In heterogenous environments storage is available to various platforms. Virtualization operations do not place any additional load on servers. Manufacturer specific configuration and implementation - proprietary. Storage devices of different manufacturers working together is difficult. Without additional server software storage virtualization cannot be expanded.

Storage virtualization in the network Advantages Disadvantages Virtualization can be extended to storage devices of different manufacturers. Virtualization is available to different servers with different OS. Advanced functions can be used even if devices do not support. Administration from central point. Neither load server nor storage devices. Additional hardware and software required. Virtualization entity can become a performance bottleneck. Less systems in production environment.