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Storage tips: the differences between file, block and storage virtualisation

Quoting ComputerWeekly 

There's a lot of confusion around file virtualisation, and virtualisation in general, because the term virtualisation can mean so many different things.

But, when we talk about file virtualisation, the focus is on file-level activities rather than block- (storage) level activities, like what you'd have in a Fibre Channel, iSCSI or direct-attached storage. But, we can break it down even further into three main areas: abstraction, emulation and aggregation. Abstraction refers to things like data movement, migration or copying. Emulation lets other devices seamlessly integrate with other applications or platforms. Aggregation lets one device sit in front of and combine multiple data streams or features.

The confusion comes in the notion of a global or clustered namespace that is actually a virtualised namespace -- think of it as a virtualised directory. As an example, consider DNS within a Windows file sharing or CIFS environment. Within a UNIX environment, there's an NIS implementation. This is the ability to see, in a single namespace, all the different file systems that are a part of that large "address space." As another example, the Internet may use a ".com" as a global designation for a URL. Don't confuse this with a global file system.

Ultimately, file virtualisation is the ability to virtualise a file-type environment. This can be done by replication, migration, data movement or any number of other file-centric features. The general features are the same as you'd see in a block environment, such as transparent data movement and device emulation for interoperability; the difference in file virtualisation is that you're dealing with files rather than blocks.

If adefinition of file virtualization is broad enough, it might include HSM capabilities. Embracing ILM is a bit trickier, because ILM is so broadly defined already.

But, generally speaking, one of the basic premises of HSM is the ability to archive or move data off to another location. HSM leaves a stub file where the data was so that the application "thinks" the data is still there. At the same time, we can define virtualisation as having emulation, aggregation and abstraction attributes. .

This is slightly different from archiving (aka data movement) in which the files and directories are moved completely.

Read the original, here.

Published Saturday, June 16, 2007 7:38 PM by David Marshall
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