Functional Differences between Disk/LUN and NFS
In a Network File storage, each virtual disk file has its own input/output queue which is directly managed by the NetApp FAS system while in logical unit number (LUN) data store it does not allow the storage arrangement to identify the input/output load generated by the individual virtual machine (Tate, 2002). In a Network file storage each virtual machine is a file or a few files which are hosted by the filer while in LUN data store, the VM appears as a single file to the filer regardless of how many virtual machines are in the LUN data store (Yang & Shekhar, 2017). Network file storage share files and data over a network connection unlike disk/LUN which share files and with the virtual machine attached hardware and software.
Virtual Storage Appliance (VSA)
A virtual storage appliance is a storage controller, managing or directing the flow of data between the entities, running on a virtual machine to form a shared storage without having to incur the cost of adding any other extra hardware devices (Tate, 2002). Virtual storage appliance can utilized free storage in a virtual machine by acting as a virtual machine storage or by acting as a direct storage for the virtual machine, they consolidate directly attached capacity on each and every physical device thus forming virtual storage pools (McCarty, 2015). They are highly applied in small businesses that require shared storage for redundancy and high availability. They are also used by large businesses entities while migrating data between different arrays (Zhang et al 2011). Examples of virtual storage appliances include; StarWind virtual SAN, FreeNAS, HPE StoreVirtual, Nimble Virtual Array and Open Filer Unified storage.
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Yang, K. S., & Shekhar, S. (2017). Spatial network big databases: Queries and storage methods. Retried from: https://www.flackbox.com/list-vsa-virtual-storage-appliance
Zhang, T., Du, Z., Chen, Y., Ji, X., & Wang, X. (March 01, 2011). Typical Virtual Appliances: An optimized mechanism for virtual appliances provisioning and management. The Journal of Systems & Software, 84, 3, 377-387. Retrieved from: https://en.wikipedia.org/wiki/Network_File_System