DFS stands for a distributed file system. It is a file system that allows multiple hosts sharing via a computer network to access files. As such, multiple users on multiple machines can share files and resources. Microsoft offers it in their Windows Server operating systems. The two main components of DFS are Namespaces and Replication.
DFS Namespaces allows users to group shared folders that are on different servers and relocate them into one or more logically structured namespaces. Each namespace is a single shared folder with a series of subfolders. This means that instead of routing users through a wide area network, they are instead automatically connected to the shared folders in the same Active Directory Domain Services site, which increases availability. DFS Replication is a multiple-master replication engine that syncs folders across servers that have limited bandwidth network connections.
Large network administrators will be interested in using a distributed file system when they want to organise and increase the availability of shared folders through use of namespaces. It also lets admins synchronise folders between servers efficiently.
Measuring performance in a distributed file system is calculated by how long it takes to fulfil user requests. In standard systems, this relies on a disk access time and how long it takes for the CPU to process the command. However, in a distributed file system, there is a difference in time due to the structure of the system. Variables include things like how long it takes for the request to be delivered to the server and the time it takes to give the client a response.
Transparency is built into distributed file systems so that files are seen as being the same as if they were on a local disk. As such, the complications of the system, like the multiplicity and dispersion of servers and storage devices, are hidden. The distributed file system seeks out the files and transports the data to the users and programs. If using concurrency transparency then it means that everyone sees the same file system state; if a file is being modified then it will be reflected across the system.
DFS offered by Windows offers a number of features. One of these is called Content Freshness, which stops a server that has been offline for a long period of time over-writing new data when it regains connectivity with out of date data. There is also recovery support from when there is an unexpected shutdown to the system. This can be a crash in the DFS Replication process due to insufficient resources, if the volume hosting the DFS Replication is dismounted, or a loss of power to the computer itself. Unexpected shut downs like these can cause the NTFS file system to lose changes that hadn’t yet been copied to the disk, making the Replication database out of sync with the file system state on the disk. From Windows Server 2008 onwards, there is usually not any need to perform the time consuming process of rebuilding the database.
What is DFS?
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