There have been many new advancements in Windows Server technologies in the past few Windows Server releases. Many of these have improved upon the core features of Windows Server, including the resiliency and high-availability features it offers. One of the newer features found in Windows Server is Scale-Out File Server (SOFS).

Scale-Out File Server is a great feature that provides highly available file-based storage that can be used for a number of different use cases.

In this post, we will take a deeper look at Scale-Out File Server.

  • What is it?
  • How does it work and how is it configured?
  • What improvements have been made with SOFS in Windows Server 2019?

These and other topics will be discussed.

What is Scale-Out File Server?

Windows Server Failover Clustering has been a good general clustering technology for hosting access to files and folders. However, as new technologies came along such as virtualization (Hyper-V) that required more robust features such as the ability to handle open files, general file-server clustering came up a bit short.

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In the case of virtual disks backing guest operating systems housed on Hyper-V hosts, there was a need for a more robust and capable clustering technology. Virtual disk files are a great example of resources on which you want to have even greater redundancy and resiliency. Scale-Out File Server (SOFS) was designed to provide resiliency to resources such as backing Hyper-V virtual machines.

With Scale-Out File Server, you can effectively satisfy the requirement of continuous availability as opposed to high-availability. In other words, you want the resource housed on the Scale-Out File Server to be available no matter what, even when you have a failure.

Scale-Out File Server (SOFS) provides a robust infrastructure platform on which to support highly-available virtual machines running in a Hyper-V environment. SOFS provides the underlying storage to Hyper-V with the capability to have multiple nodes online in an active-active configuration with persistent connections between the nodes.

The tremendous benefit to this is if a server providing storage to the Hyper-V environment goes down, the others immediately take over providing storage for the virtual disk files. This does not involve a cutover or migration process to get the data to the other servers. With SOFS backing Hyper-V storage, the virtual machines are able to stay online after a failed storage server with the backing of Scale-Out File Server.

Benefits Afforded by Scale-Out File Server

What are the benefits you gain by using Scale-Out File Server (SOFS)? These include the following:

  • File shares are active-active – This means that all cluster nodes can accept and serve SMB client requests. A tremendous benefit of the active-active topology of the SOFS cluster Is failovers are transparent to alternate cluster nodes that assume the file share. This means if you have a Hyper-V cluster using SOFS, the VM stays online during a failover
  • Increased bandwidth and performance – The bandwidth and by extension the amount of performance you get out of your SOFS backed file shares are linear to the number of nodes that are added to the cluster. In a traditional file cluster, the total bandwidth is no longer constrained to the bandwidth of a single cluster node. You can increase bandwidth by simply adding hosts to the cluster
  • CHKDSK does not require downtime – CHKDSK general requires having exclusive access to the file system. However, the Cluster Shared Volume aspect of SOFS eliminates the downtime by no longer needing the offline phase. The Cluster Shared Volume File System (CSVFS) can use CHKDSK without impacting applications with open handles on the file system
  • CSV Cache – Cluster Shared Volume cache is read-cache introduced in Windows Server 2012 that significantly improves performance in certain scenarios like VDI infrastructures
  • Easier management – Management has been simplified. You need not create multiple clustered file servers, with separate cluster disks and then develop placement policies. Now you can create the SOFS and then add the CSVs and file shares
  • Automatic Rebalancing of the Scale-Out File Server clients – With Windows Server 2012 R2 automatic rebalancing improves the scalability and manageability for SOFS. SMB connections are tracked per file share and then clients are redirected to the cluster node with the best access to the volume used by the file share. This helps to improve efficiency

How Scale-Out File Server Works

Scale-Out File Server allows creating shares that allow the same folder or file to be shared from multiple cluster nodes. If setup to use SOFS and SMB 3.0, the VMs housed therein can be accessed with a simple UNC pathname.

SMB 3.0 manages the load-balancing of the solution as well as the redundancy and management of the network for fault tolerance. These technologies allow the solution to be an active/active solution so performance is linear to the number of servers backing the SOFS share name.

As already mentioned, continuous availability is afforded by SOFS and ensures the integrity of your data by using synchronous writes. It allows you to have up to 8 nodes backing the SOFS share.

Prerequisites

There isn’t a long list of prerequisites for implementing Scale-Out File Server. However, the following are ones to note.

  • Windows Server Failover Cluster compatible storage
  • File Server Role installed on your SOFS hosts
  • SMB 3.0 (Must be Windows Server 2012 or higher so SMB 3.0 is available)
  • Active Directory infrastructure
  • If you are using pre-Windows Server 2019 version of Windows Server, loopback configurations are not supported. This means housing Hyper-V and the SOFS file server on the same server

Architecture Overview

Below, a simple view of Hyper-V accessing a SOFS file share hosted between two SOFS nodes.


Simple overview of Hyper-V connected to SOFS (image courtesy of Microsoft)

Another view of an extended configuration of Hyper-V connected to SOFS.

Multiple Hyper-V nodes connected to SOFS (Image courtesy of Microsoft)

Multiple Hyper-V nodes connected to SOFS (Image courtesy of Microsoft)

New Scale-Out File Server Features in Windows Server 2019

Windows Server 2019 has brought about many enhancements to Scale-Out File Server. These make SOFS in Windows Server 2019 the most resilient and performant SOFS version to date. What enhancements are found in Windows Server 2019 SOFS?

Traditionally, SOFS is heavily reliant on DNS round robin for the connections coming inbound to cluster nodes. This can result in a few inefficient operations. For instance, if a connection is routed to a failover cluster node that is not the owner of a Cluster Shared Volume (CSV), data is redirected over the network to another node before returning to the client. The SMB Witness service detects the lack of direct I/O and moves the connection to a coordinator node (CSV owner) which can lead to delays in returning data.

Windows Server 2019 provides a much more efficient behavior when it comes to returning data. The SMB Server service determines if direct I/O on the volume is possible. If it is, it passes the connection on. If it isn’t (redirected I/O) it will move the connection to the coordinator before I/O begins. There is a limitation in which clients/Server connections can use this new functionality. Currently, it is limited to Windows Server 2019 and Windows 10 Fall 2017 clients.

A new SOFS role in Windows Server 2019 is called the Infrastructure File Server. When created, the Infrastructure File Server creates a single namespace share automatically for the CSV drive. In hyper-converged configurations, the Infrastructure SOFS role allows SMB clients such as a Hyper-V host to communicate with Continuous Available (CA) to the Infrastructure SOFS SMB server.

Another enhancement in Windows Server 2019 with the SMB Loopback where SMB can now work properly with SMB local loopback to itself. This was not supported previously. hyper-converged SMB loopback CA is achieved via Virtual Machines accessing their virtual disk (VHDx) files where the owning VM identity is forwarded between the client and server.

Cluster Sets are able to take advantage of this where the path to the VHD/VHDX is placed as a single namespace share which means the path can be utilized regardless of whether the path is local or remote.

With Windows Server 2016, Hyper-V compute hosts have to be granted permission to access the VHD/VHDX files on the SOFS share. However, with Windows Server 2019, a new capability called Identity Tunneling has been introduced to allow permissions to be serialized and tunneled through to the server. This greatly reduces the complexity of the permissions for accessing the SOFS share for each Hyper-V host.

Let’s take a look at configuring Scale-Out File Server in a Windows Server 2019 Hyper-V cluster.

Configuring Scale-Out File Server in Windows Server 2019

The process to configure the Scale-Out File Server is found in the Failover Cluster Manager. Currently, Windows Admin Center does not contain the ability to manage SOFS as detailed here, however, it most likely will be added as a functional feature in an upcoming release. We will look at what you can currently see regarding SOFS in Windows Admin Center below.

To get started configuring Scale-Out File Server in Failover Cluster Manager, right-click Roles and select Configure Role. This will launch the High Availability Wizard where you select role you want to add as a clustered role. Select File Server. For our walkthrough, we are configuring SOFS for the purpose of backing Hyper-V VMs.

Keep in mind, this will not automatically add the Windows Role (File Server) to your Windows Failover cluster hosts. You will need to add the underlying Windows Role to your hosts before running the High Availability Wizard for your cluster.

Beginning the Select Role wizard

Beginning the Select Role wizard

After selecting the File Server role, you will need to choose the File Server Type. The options for your File Server configuration are:

  • File Server for general use
  • Scale-Out File Server for application data

We are interested in the second option which is Scale-Out File Server for application data. As per the description notes, you will want to use this option to provide storage for server applications or virtual machines that leave files open for extended periods of time. Scale-Out File Server client connections are distributed across nodes in the cluster for better throughput. This option supports the SMB protocol. It does not support the NFS protocol, DFS Replication, or File Server Resource Manager.

Choosing Scale-Out File Server for application data

Choosing Scale-Out File Server for application data

After choosing the SOFS file server option, you will choose a name for what is referred to as the Client Access Point. This will be reflected in the cluster resource as well as the SOFS file share.

Configuring the Client Access Point

Configuring the Client Access Point

Confirming the options configured in the High Availability Wizard with the Scale-Out File Server configuration.

Confirming the addition of the Scale-Out File server clustered role

Confirming the addition of the Scale-Out File server clustered role

The summary screen will detail the options configured.

SOFS is successfully configured as a clustered role

SOFS is successfully configured as a clustered role

Adding an IP Address Resource to the SOFS Role

Adding an IP Address Resource to the SOFS Role is a straightforward process. Simply right-click on the SOFS role name in Failover Cluster Manager, choose Add Resource > More Resources > IP Address.

Adding an IP Address resource to the Scale-Out File Server

Adding an IP Address resource to the Scale-Out File Server

There are a couple of additional steps to get the IP Address resource for the SOFS role configured. First, you need to actually assign the IP Address you want to use as well as the Network associated with the IP Address.

Configuring the IP Address and Network for the new IP Address resource

Configuring the IP Address and Network for the new IP Address resource

After you configure the IP Address resource for the SOFS role along with the network it belongs to, you will need to Bring Online the IP Address resource. Simply right-click the IP Address and choose Bring Online.

Bringing the SOFS IP Address resource online after configuration

Bringing the SOFS IP Address resource online after configuration

Adding a File Share to Scale-Out File Server

After you have configured the SOFS role as well as added the IP Address resource, you need to configure the File Share that will be made continuously available. To do this, right-click your Scale-Out File Server role name in Failover Cluster Manager and choose Add File Share.

Beginning to Add File Share to the Scale-Out File Server

Beginning to Add File Share to the Scale-Out File Server

This launches the New File Share wizard. The first part of the configuration for the Scale-Out File Server share is to select the profile for this share. The options include:

  • SMB Share – Quick
  • SMB Share – Advanced
  • SMB Share – Applications
  • NFS Share – Quick
  • NFS Share – Advanced

For use with Hyper-V and database applications, here we are selecting SMB Share – Applications. This profile creates the SMB file share with settings appropriate for Hyper-V and database applications.

Selecting a file share profile for creating the new SOFS file share

Selecting a file share profile for creating the new SOFS file share

Select the server and path for this share.

Select the server and path for the SOFS file share

Select the server and path for the SOFS file share

Next, you need to specify the share name. The share name you choose is reflected in the remote path to share.

Specifying the share name for the SOFS file share

Specifying the share name for the SOFS file share

On the Configure share settings screen, you will see a number of configuration settings related to share configuration. By default, the SMB Share – Applications will have the Enable continuous availability selected. This allows continuous availability features to track file operations on a highly available file share so that clients can failover to another node of the cluster without interruption.

As mentioned earlier, this means virtual machines can continue operating without interruption despite a host failure in the Scale-Out File Server storage nodes. As you will see below, there are many other options that can be selected as well, including encrypt data access.

Enabling continuous availability for the new SOFS file share

Enabling continuous availability for the new SOFS file share

Next you can specify permissions to control access to your SOFS share.

Configuring permissions to control access

Configuring permissions to control access

Lastly, confirm the selections made in the New Share Wizard.

Confirm selections for creating the SOFS file share

Confirm selections for creating the SOFS file share

The new share wizard completes with the SOFS file share created successfully.

SOFS share created successfully

SOFS share created successfully

Now, in Failover Cluster Manager, you can look at your SOFS resource Shares tab and see the new file share created and listed.

Confirming SOFS shares in Failover Cluster Manager

Confirming SOFS shares in Failover Cluster Manager

Storing Virtual Machines in an SOFS File Share

When creating a new Hyper-V virtual machine, you can store the virtual machine on an SOFS file share simply by specifying the file share in the Location box in the Specify Name and Location step of the New Virtual Machine Wizard. This is in the form of a UNC path.

Creating a new virtual machine using the SOFS file share location

Creating a new virtual machine using the SOFS file share location

As you can see, after specifying the UNC path for the SOFS share in the Location, you will see the full path created for your individual virtual machine on the SOFS share.

Location of virtual machine disks reflected in the New Virtual Machine Wizard

Location of virtual machine disks reflected in the New Virtual Machine Wizard

Windows Admin Center

We had touched on this a bit earlier. What about the Windows Admin Center configuration? At this point, Windows Admin Center does not allow the configuration of SOFS that is needed. However, you can view your cluster roles as well as the details of your SOFS role inside of Windows Admin Center.

Like many other Windows technologies, Microsoft is no doubt working on getting SOFS configuration as well as many other configuration tools inside of Windows Admin Center. It will only be a matter of time before you will be able to fully configure SOFS inside of Windows Admin Center.

Viewing your SOFS role information inside of Windows Admin Center

Viewing your SOFS role information inside of Windows Admin Center

When To Use And When not To Use A Scale-Out File Server

Scale-Out File Server is extremely powerful and can satisfy many use cases. What are some typical use cases where SOFS is a good fit, and also where might it not be a good choice for a backend storage technology? Let’s consider this topic.

So, when is a good use case for Scale-Out File Server? Well, the screen in the High Availability Wizard gives the clue to where SOFS fits best – application data. This includes Hyper-V and SQL Server.

SOFS adds the ability to have active-active, highly available storage via SMB 3.0. With SOFS, the server synchronously writes through to the disk for data integrity which provides resiliency in the event of a host failure. If you were to “pull the plug” on your SOFS server, it helps to ensure that your files will be consistent.

With Hyper-V and SQL workloads, the file operations are not very metadata intensive. This means the extra overhead of the synchronous writes that comes with Scale-Out File Server does not really impact the performance of your Hyper-V or SQL workloads.

This helps to highlight when you would not want to use the Scale-Out File Server. In typical end-user environments where there are a tremendous number of file operations including the normal “file opens, file deletes, editing”, and so on. According to Microsoft, this can lead to frequent VDL extension which can mean quite a bit of disk operation overhead, via SMB operations.

As we already know, continuous availability (CA) requires that data write-through to the disk to ensure integrity in the event of a host failure backing SOFS. These synchronous file writes mean there is an impact on write performance. A large VHDX or SQL Server database file also experiences the overhead on file creation time, however, generally, the space for these types of applications is preallocated so disk I/O is comparatively much lower for these.

Another important thing to note is, you can’t use DFS replication to replicate a library share hosted on a scale-out file share.

Concluding Thoughts

Scale-Out File Server provides a really great way to have active-active storage high-availability along with resiliency without expensive storage hardware. Performance scales along with the number of nodes that are added to the SOFS-backing servers. Creating a SOFS infrastructure configuration is easily achieved with only a few clicks in the Failover Cluster Manager with Windows Admin Center functionality soon to come.

As discussed, SOFS is not for every workload. It is best suited for Hyper-V and SQL application data. General file I/O as is the case with normal file opens, edits, deletes and such as is experienced with general-purpose end user file activity is not well-suited for the synchronous write overhead of SOFS. With these types of workloads you will most likely want to house these on traditional file server infrastructure.

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