Which storage replication mechanism is used by Windows Server in multi site failover cluster?

Sometimes you have to choose which technology is most suitable for your environment. Other times you wonder if you should replace an old technology already use with a new one. 

I spent a few weeks researching to find out how to decide when to use Storage Replica or DFSR(Distributed File System Replication)?

Let's take a look at which situations you can use DFSR(Distributed File System Replication) or Storage Replication.

DFSR(Distributed File System Replication)

DFSR is an old technology that was first introduced in Windows Server 2003. However, today many companies continue to use it as a File Server replication solution between Branches.

Wondering why they keep using an old technology? Why they don't replace with a new one like Storage Replica ?

Let's take a closer look !!

What is DFSR ?

• Multi master replication engine. Multi-master replication is a method of database replication that allows data to be stored by a group of computers, and updated by any member of the group. All members are responsive to client data queries. The multi-master replication system is responsible for propagating the data modifications made by each member to the rest of the group and resolving any conflicts that might arise between concurrent changes made by different members. 

When to use it and when not to use it.

This is a difficult question with a more difficult answer. You can read the following list to understand if meets your requirements.

• You can use it with limited bandwidth between 2 Offices. If you have 2 Offices connected very usefully when you have limited bandwidth between your Offices.

• When you have Office in different physical locations and you would like to centralize your file Server.

• Don’t use DFSR when multiple users need to modify the same files at the same time on different servers. Doing so can cause DFS Replication to move conflicting copies. Believe you don't want this.

What are the limitations of the DFSR?

• Windows and DFS Replication support folder paths with up to 32 thousand characters. DFS Replication is not limited to folder paths of 260 characters.

What it can do and can't do.

• Replicate only the changed file blocks instead of the entire file.

• It’s not has a lock mechanism. What exactly does this mean? Let's explain it. You have 2 users that opened the same file. The 2nd user did some changes and close the file. After the first user did a few changes in the same file and close it. The changes from the 1st user will be override the changes of the 2nd user. The 2nd user will be lost all the changes. That is very bad !!!1

• Files must be closed to replicate. 
• DFSR can replicate files between multiple file servers. Handy when you have users working in different locations.

I hope to give you understand if DFSR is for suitable for your environment

Storage Replication

Storage replica is a new technology that was first introduce in Windows Server 2016 Datacenter edition only. Enable replication of volumes between servers or clusters.

Let's take a look in more details !!!

When to use it and when not to use it.

Storage Replication is a great solution but can't be use it for any environment.

• You can use it when you want to have a Disaster Recover Solution for your Clusters.
• When you want to have a Disaster Recovery Solution for your File Servers
• When you want to do Cluster to Cluster Replication.

• When you want to do Cluster to Cluster Storage Replica cross region in Azure.

• For Cluster to Cluster Storage Replica within the same region in Azure

• For Stretch Cluster Replication using Shared Storage.

• You can't use it to centralize your File Server in Branches to different locations.

What are the limitations of the Storage Replica ?

• Needs enough bandwidth and an average of 5ms round trip latency or lower for synchronous.

• Storage Replica can use it with Windows Server 2016/2019 Datacenter Edition only. Microsoft announced that include Storage Replication in Windows Server 2019 Standard edition but only for 1 volume and up to 2 TB. However I didn't hear any change in Windows Server 2022.

What it can do and can't do

• Storage Replica It’s a block level replication.

• Support synchronous or asynchronous replication.

• Support seeded initial sync. When a subset of data already exists on a target, initial replication copies only the differing blocks.

I hope ι gave some clear advice to understand where to use DFSR or Storage Replica.

Have a nice weekend

What is a multi site failover cluster?

What is Windows Server Failover Clustering?

What is cluster cluster replication?

What is failover cluster storage?