What is File System Virtualization?
File virtualization refers to storage virtualization technology that involves developing an abstraction layer between the file server and the users that access those files. File system virtualization helps developers to publish only relevant shared folders and to provide authentication-based private folders. Through file system virtualization, users are able to access files and folders thar are located on multiple servers as if they were all located in the same place, allowing data to be moved without disrupting user access. There are two different kinds of file virtualization systems1:
In-band. In-band storage virtualization occurs when the virtualization engine operates between the host and storage. Both input/output (I/O) requests and data pass through the virtualization layer, which allows the engine to provide advanced functionality like data caching, replication, and data migration. In-band takes up fewer host server resources since it does not have to find and attach multiple storage devices. The server only sees the virtually pooled storage in its data path, but larger pooled storage pools present higher risks that it will impact data path throughput.
Out-of-band. Out-of-band storage virtualization splits the path into control (metadata) and data paths. Only the control path runs through the virtualization appliance, which intercepts I/O requests from the host, looks up and maps metadata on physical memory locations, and issues an updated I/O request to storage. Data does not pass through the device, which makes caching impossible. Out-of-band virtualization installs agents on individual servers to direct their storage I/O to the virtualization appliance. Although this adds to individual server loads, out-of-band virtualization does not bottleneck data like in-band could. Best practices are to avoid virtualization disruption by adding additional redundant out-of-band appliances.
Advantages of file system virtualization include:
- Better availability and flexibility to end users
- Lower overall cost of storage capacity
- Scalability
- Fast deployment
- Simplified data center management
- Having a global namespace to index files on network file servers
- Minimized or eliminated downtime
- Increased IT productivity and responsiveness
- The ability to overcome file system size limitations by allocating storage for files on various servers
- Faster provisioning
- Providing storage management for network-attached (NAS) and storage area network (SAN) storage systems
1 Taylor, 2020, “Storage Virtualization”