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What is the difference between DFS and cluster replication?

Posted on 2011-03-24
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What is the difference between DFS and cluster replication?
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Question by:SAM2009
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DFS or Distributed File System uses several different disk locations that replicate the same data to each other. This is good if you have two or more locations (different sites) and you want users and applications to access the data in the site that is closest to them.

If you are talking about a Microsoft Cluster then you have a situation where the same disks are being shared by multiple computers. Data is not replicating it is being shared.

CCR Continuous Cluster Replication is the process where data is maintained at two different sites by having only the changes of 1 site automatically replicating to the other sites to keep them all in sync. This is used for failover and data redundancy.

If this doesn't answer your question that you will have to be more specific on what you mean by cluster replication. There are several different types used for different reasons.
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by:Nick67
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DFS is Distributed File System.
Lets say that you have 20 servers with 20 shares.
Mapping out 20 drive letters would be a pain and then end-users would have to know what stuff was in each share.
DFS lets you map all those disparate shares under a single 'root' share
The end users no longer need to know or care what server or share that stuff is in, it just looks like a single drive with folders.
Moreover, the admin can move stuff between the servers, and change the shares, but the end-users see no change.

Cluster replication is when you have multiple physical servers sharing access to a single, typically SAN, storage system.
The end user neither knows, nor cares, which server it is hitting.  The servers can round-robin, in fact.

DFS is not really about disaster recovery, per se.
Because the shares are masked by DFS, if you have a failure, you can restore the share of the bombed machine to some other server, update DFS and carry on with little interruption.  But your server is bombed, and you do have to restore and configure.

Clustering has multiple machines serving data from a single source.  So a server bombing changes nothing--one less server serving up data, but no outage or reconfiguration required.  Restore your server, add it back in the cluster, replicate the data back to it and its go time.

Now, because the SAN could bomb, there is replication.  This provides redundancy in case the joint data store buys it.  The setups vary, but the idea is that the multiple physical servers get seen as a single unit.  Any element bombing, a server or the SAN, doesn't cause and outage because the whole system is set up in anticipation of such events and is meant to deal with them.  Some setups don't have the SAN, they just have drives on the servers. But, the idea is the same.  Pull the plug on any server in a cluster and the end user doesn't know anything has happened.  Clustering is all about high availability.

Pull the plug on the server serving DFS and everything is likely to go down.  Pull the plug on any server contributing shares to the DFS and those shares will be offline until a restore operation is completed.  Offline can mean not accessible, but it can also mean that changes to files are held and sync'ed when the share comes back online.  So there is some element of disaster recovery to DFS--but DFS is more about administration and logical grouping of disparate resources than about high availability
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DFS synchronizes/copies data to several locations so multiple servers have their own copy. This is usually just for synchronizing files, nothing else.

Cluster replication is not several servers sharing the same drives. it is a group of servers that continuously copy each others settings and configurations to that they can cover for each other if one fails.
This usually covers almost all aspects of the settings/configuration/data and is similar to how Domain controllers copy the entire Active directory configuration and can all share the load or continue working if one fails.

DFS > synchronizing shared folders or files between several servers.

Cluster > having entire servers (often exchange servers) as a backup for failure or to share the load out.
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by:ChiefIT
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DFS stands for distributive File shares. They are a group of shares that are under a common root file folder. They are replicated to different servers using DFSR (Distributive File Share Replication). These shares are distributed out using Netbios. But, DFSR uses DNS to locate the servers the data is replicated to or from. Netbios broadcasts will show the file shares in My Network Places. The two servers will have the same set of files after Replication. That set of files within the staging point is called a namespace:

Cluster replication would would more equivelant to having two domain servers in a cluster. In fact, let's use that as an example. That process uses File Replication Service, (FRS). FRS is used to copy AD, DNS and other server important activities to make your servers appear as ONE or at least have the exact same important server data. In other words, FRS is used to replicate server critical data to make those servers have the same data and function the same in your LAN.

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by:Nick67
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The author posted for Server 2003
The more WAN/replicative parts are an R2 innovation
http://www.microsoft.com/windowsserversystem/dfs/default.mspx

DFS is a technology concerned with simplifying the ease of access and administration of file shares
Clustering concerns itself soley with high availability.
DFS, by its nature, has some fault-tolerance strengths

The author posted under disaster recovery
DFS is not intended as a DR solution
Clustering solutions, like Sunbelt Software's Double Take amongst others, are intended for DR.

The 10,000 ft. view :)
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by:SAM2009
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Hey guys sorry for the delay...many thanks fro all your explanations!
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