Posts Taged hybrid-datacenter

Azure Stack HCI Mirror vs Nested Volume Performance

Got a two node Storage Spaces Direct Cluster? Then Windows Server 2019 can bring you more resiliency with the same hardware, but how does it perform…

Two nodes are popular

The adoption of Storage Space Direct and Azure Stack HCI clusters is growing month by month. Over the years the two node clusters became very popular. But with only two nodes you are a bit more at risk. Your precious data is only available on two nodes. And when disaster strikes and you lose 1 disk in both nodes, or a node and a disk….volumes go offline ☹.

Windows Server 2019 brings new forms of volume resiliency to the table in the form of nested resiliency. The new nested resilicency comes in two new flavors of resilience “Nested Mirrored Volumes” and “Mirror Accelerated Parity Volumes”.


This blog is not to explain all the details about nested resiliency. Microsoft already did a great job for us here. Feel free to check it out. But to make this blog more clear to our readers, we provide a little background information.

In Windows Server 2016 Storage Spaces Direct we have these 4 resiliency options available to create volumes.

Based on the amount of nodes you have in your cluster, you can choose a form of resiliency.


With two nodes you can have two copies of the data. With three nodes you can have three copies of the data. Which means you can either lose one node or a disk in a node in a two-way mirror. Or lose two nodes or a disk in two of the three nodes in a three-way mirror without volumes going offline. With three nodes and above you can stick with the three-way mirror.


In the case of single parity it’s just like in the traditional RAID5 configurations. Blocks are written and parity data is calculated and written on another node. With dual parity there is more parity data to sustain more failures. Single parity requires three nodes and can sustain a node failure or disks in one node. With dual parity you need a minimum of four nodes and you can of course lose two nodes or disks in two nodes.

Volumes with parity are great for efficiency in disk space but they have a terrible performance and are only considered valid in backup or archival environments.

New Resiliency options

Based on the amount of nodes, some options are not available. In the case of a two node cluster there is only one option left! And that is the two-way mirror. Because of that, Microsoft added two additional resiliency options specifically and exclusively for the two node cluster configurations.

Nested Mirror

With a nested mirror you basically create a local and a remote mirror in one volume. So your volumes stripes across two nodes like a regular mirrored volume. But the block your write is not only available on another node, it is also copied on the same node and twice on the remote node. The picture below gives a good understanding:

In this case you can not only lose a node, but also a drive on the remaining node . With the nested mirror volumes you are much more resilient and can sustain more drive losses then in a two-way mirror. Unfortunately it is not efficient and you have only 25% of capacity available, but if availability is critical this is your way forward.

Nested Mirror Accelerated Parity

The second new flavor there is, is nested mirror accelerated parity…. Let’s explain that first by showing it in a picture.

When you create a nested mirror accelerated parity volume the storage does a little trick. Because part of that volume contains mirrored storage, let’s say 20%. The other 80% of the volume is created as a Parity. And then both parts are also copied to the second server. This way, the storage consumptions is much more effective because 80% is parity and 20% nested mirror. The storage uses the mirrored part of the volume as cache to improve performance and moves it to the parity part of the volume after it has been written. Pretty cool! But how does it perform? That is a question we have received a lot, so we tested it!

Testing Parameters

We use VMFleet and DiskSPD to test the performance of the different volumes. With these tools, we can quickly create a large amount of VMs and disks that we use for testing. When the VMs are deployed you can start the load tests on all the VMs simultaneous with a single command. During our tests we used the following test parameters:

  • Outstanding IO: 8

  • Block Size : 4k / 8k / 64k

  • Threads : 10

  • Write: 0% / 30% / 100%

  • VMs: 14 VMs per node

We then run 3 series of tests per type of volume. So the first test is based on 4k blocks. Thereafter we run a 100% read, 70% read and 0% read test. We repeated this process based on 8K blocks and so on, until the 64K blocks size. That results in a total of 9 tests.

Mirrored Volume Test

In this first test we created 2 mirrored volumes of 600GB and deployed 14 VMs to each volume. After that we started the series of tests with the parameters above. See the diagrams below for details.  

Nested Mirrored Volume

For our second test, we now create 2 nested mirrored volumes of 600GB each and deployed the 14 VMs to each volume. We then run the same tests as before which gives us the following results.

Nested Mirror Accelerated Parity

In the last test we again create 2 volumes, but this time nested mirror accelerated parity volumes. The mirror part is 100GB and the parity part is 500GB. We then deployed the 14 VMs to each volume. After that we started the series of tests with the parameters from before.


As we can see in the tests displayed above we have little to no performance loss when we only read data from a Mirrored Volume, compared to a Nested Mirror volume. Because not all the data is in the mirrored part of the Nested Mirror Accelerated Parity volume, we see a bigger performance drop when we read data. When the data set you read is smaller and/or your mirrored part of the volume is bigger, there should be very little performance difference. 

When we start writing data you see differences in performance which is very logical. In regards to the nested mirror volume we lost half of our physical disks that we can write to because of extra mirroring. In addition to that, creating more copies takes more time. The nested mirror accelerated parity volume is of course slower because a lot of parity calculations have to take place which gives a big performance hit, especially with write operations.


If you need the added resiliency of Windows Server 2019 with nested resiliency and a good amount of disk capacity, it is better to invest in additional storage and use nested mirror volumes. Going forward with nested mirror accelerated parity is not advisable for VM workloads.

Want to know more or do you have questions about Nested Resiliency then drop us an e-mail.

    Azure Stack HCI local vs stretched volume performance

    Azure Stack HCI OS Stretched Clustering

    One of the great new features in Azure Stack HCI OS is stretched clustering support for Storage Spaces Direct (S2D). With stretched clustering you can place S2D nodes in different sites for high availability and disaster recovery.

    While in Windows Server 2019 you already have the ability to use stretched clustering, it was not yet possible with S2D enabled hosts. With the arrival of Azure Stack HCI OS, there is no holding back and we can now benefit from stretched clustering for hyper-converged systems!

    As you might have heard or read about here, Azure Stack HCI will move forward as a new operating system with integration to Azure. In the new Azure Stack HCI OS there are lots of new features that we tried before and during public preview. It is important to understand that we did the testing with a preview version that is released as Azure Stack HCI 20H1. Performance on the GA version can be different.

    Stretched clustering for HCI, is a very welcome feature and requested by a lot of customers for a long time. But are there differences in performance in compare to single site clusters? We too were curious about the performance differences and did some testing.

    Stretched Volumes

    Before we start testing, first a little bit of background info. When hyper converged nodes are stretched across 2 sites, you have the ability to stretch the volumes across the sites. While it seems like there is only one volume, if you dive below the surface you will see multiple volumes. Only one volume, the primary volume, is accessible from both sites at the same time. The secondary volume in the other site is standby for access and only receiving changes from the primary volume. This is just like in any other stretched or metro cluster solution. When disaster strikes the primary volume goes offline and the replica is brought online in the other site. The VMs fail over and start so the applications are accessible again.

    When you create a stretched cluster and are ready to deploy volumes, you have 2 options: you can either create an asynchronous or synchronous volume. More info on which option to choose is described in the next chapters.


    With an “Asynchronous” volume the system accepts a write on the primary volume and responses back with an acknowledgement to the application after it is written. The system then tries to synchronize the change to the replica volume as fast as possible. It could be milliseconds or seconds later that the replication is finished. Depending on the amount of changes and intervals of the system, we could lose x amount of changes that already have been written to the primary volume but not yet to the replica volume, in case of a failure of the primary site.


    A volume that is setup as “Synchronous Volume” will respond to the application with an acknowledgement after it has been written in both sites. The write is accepted by a node and copied to the other site. When both blocks have been written, the application will receive an acknowledgement from the storage. When the primary site fails there is no data loss since it’s in sync with the secondary site.


    To give a better understanding of what our test setup looks like we provide some extra information.

    In this case we have 4 servers that only contain flash drives. The servers are physically in the same rack but we simulated 2 sites based on 2 subnets. The primary site is called Amsterdam, the secondary site is called Utrecht.

    In this setup the servers from both sites are in the same rack and cable distance is only meters instead of several kilometers or miles. So there is no additional latency because of the distance between the sites. That is important to keep in mind.

    Both sites contain 2 servers and each server has:

    – One volume that is not replicated to the other site but only between the nodes in the same site.
    – One stretched synchronous volume
    – One stretched asynchronous volume

    Per server we have a total of 3 volumes and on each volume we deployed 10 VMs for testing.

    Testing the setup

    We use VMFleet and DiskSPD to test the performance of the volumes. With these tools we can quickly create a large amount of VMs and disks that we use for testing. When the VMs are deployed you can start the load tests on all the VMs simultaneous with a single command. During our tests we used the following test parameters:

    • Outstanding IO: 16

    • Block Size : 4k

    • Threads : 8

    • Write: 0% / 30% / 100%

    Local Volumes Tests

    First we start testing with the local volumes and boot the 40 VMs (10 VMs per volume) on the local volumes. Then we conduct the three tests based on zero writes, 30% writes and 100% writes. The results can be seen below.

    Synchronous Stretched Volumes Test

    Next, we tested the VMs that are deployed on the stretched volumes with synchronous replication. Like before we only start the 40 VMs deployed on the stretched volumes and start the same tests as before.

    Asynchronous Stretched Volume Tests

    For our last test we also use an stretched volume, but this time we used an Asynchronous volume. Again we only use the 40 VMs that are located on this volume and run the same tests.


    To wrap things up, we have put all our results from the tables above in a diagram. Now we can visualize the difference between the various types of volumes. As you can see in the diagram, there is almost no difference between the types of volumes when we only read data.

    The difference is starting to show when we start writing data. The synchronous and asynchronous volumes differences are huge compared to the local volumes. Considering these systems are next to each other, it will be worse when there is, for example, 50 km of fiber connection between the sites. 

    Note: The tests above were conducted with a 4k block size, which is considered the most intensive size for the logs to keep up. Using an 8k or 16k block size, which are considered more regular workloads, their will be less difference between the local and replicated volumes.

    Stretched clustering is a great way to improve availability for hyper-converged clusters. Although the preview build performance results are not satisfying enough. It’s good we test this in early preview stages of the Azure Stack HCI OS, so the product gets the improvements it needs before Azure Stack HCI OS gets to GA.

    If you have any questions or want more information about Azure Stack HCI OS, or stretched clustering let us know! We are happy to assist! 

      How to get your file server in Azure

      In today’s cloud orientated world, lots of File Servers lose the battle to modern solutions like Teams and Sharepoint. But what if these solutions don’t work for your company. For example, these files are not supported on those platforms or the applications working with the files don’t support accessing it from any other type of share than CIFS or SMB. Files are too big and accessed to regularly which cause latency or a too big demand on the internet connection?

      Are you out of luck and cannot take advantage of cloud services for this? Maybe not yet.. Typically, for most of the organizations 80% of the data is never to almost never accessed. What if the clients and applications require that the hot data is available with low latency? We can use Azure File Sync to move the 80% of cold data to Azure Files. This way we save disk space on storage. If all the files are stored in Azure it is also possible to store them in Azure Backup! It is most likely cheaper and automatically offsite.

      Let’s look at Azure Files and Azure File Sync!

      What is Azure Files?

      With Azure Files you have the ability to store files in Azure Storage accounts which can be presented as files shares that you can access over SMB. Microsoft put in a lot of effort the past year to enable NTFS permissions on this, and they have done a pretty good job in making it more usable now. They enabled AD integration so you can use NTFS permissions and groups now. And you can access the shares from remote offices and your datacenters with Azure Private Link. And last but not least? you can also use DFS-N (Distributed File Service Namespace) now.

      At Splitbrain we always recommend the use of DFS-N in file servers. DFS-N gives you great flexibility in case of migrations or when you need to move files and folders around to other disks or servers.

      What resources do we need?

      You can use different storage accounts based on your needs. For example in the case of availability you can use Local Redundant Storage (LRS), Zone Redundant Storage (ZRS) or go global with Global Redundant Storage (GRS). And there is a performance point of view with regular or premium storage.


      In Azure you pay for the resources you use. For Azure Files you can take a look at Azure Files pricing overview to calculate how much it will cost if you migrate your files to Azure Files. Keep in mind that not only storing the files in the share cost money. With accessing, listing and changing the files you will also be charged based on x amount of actions. In addition downloading the files from Azure Files to the client are charged as described here.

      What is Azure File Sync?

      With Azure File Sync you can extend your current file server to Azure in a tiered storage principle. You use your current file server as endpoint for your clients with all the current features there are today and offload the bulk of your data to Azure. You can configure the Azure File Sync agent to keep files newer than x amount of days on the file server per share or choose to not tier at all. This way most of the hot data is locally and only changes are sync from and to Azure.

      With Azure Files, Azure File Sync and your file server you can have best of both worlds!

      Note that you cannot use DFS-R and AFS Tiering on the same volume, they will bite each other.

      What resources do we need?

      With Azure File Sync we also require storage accounts to store the data. The same rules apply for the different types of storage accounts as described in the chapter Azure Files. On top of that we need a storage sync service to takes care of the synchronization and access of the data from the file server.


      For Azure Files information you can view the pricing chapter for Azure Files above. On top of that we also need an Azure File Sync Service (or storage sync service) and that one is free if you only use one file server. When you have more you will be charged for the additional servers. Keep in mind that most of your data that is changing is on your file server. So your operational costs will be lower with Azure File Sync in compare to Azure Files.

      Now let’s dive into that!

      Azure Files and Azure File Sync use cases

      To give you a better understanding of the possibilities with Azure Files and Azure File Sync we describe some example scenario’s below.

      Azure Files

      In this use-case the company moves all the files to Azure Files. Most of the companies keep the SMB port (445) closed to the internet. In addition, there are several ISPs that block SMB on their networks. To be able to move and access the files from the datacenter and/or office locations, we first need to setup a Site-to-Site VPN or an ExpressRoute. We also need our ADDS (Active Directory Domain Services) synced to AAD (Azure Active Directory) and enable ADDS authentication on the storage account for the file shares. The setup requires an Azure Private Link and Azure Private DNS to be able to resolve and access the Azure files shares over the ExpressRoute or VPN.

      If your company is already using several resources in Azure and you already have an ExpressRoute or VPN connection you can leverage this.

      We also need a Domain controller and DNS server in our datacenter/office and a server to host our DFS namespace. When we put all that in the mix and configure it the right way your users are able to access the file shares running in Azure.

      User A accesses the DFS Share and browse the Marketing folder. When opening the file, it is downloaded from the storage account to his device and opened.

      This scenario is great for small deployments, but this can get problematic for a number of reasons. For example when you have lots of users accessing the files. The files might be too large. These examples would have impact on the available internet bandwidth and could lead to other issues in the organization. The added latency could become a problem for some applications and the application experience becomes slow. If the internet connection is gone, so are the files. And there are more of these technical challenges to tackle when your environment is getting bigger. For these reasons Azure Files might not be the solution for your organization.

      Single file server with Azure File Sync

      We have a single file server running in your datacenter with for example 10 terabytes of storage. That takes up a lot of data on the underlying storage system and the backup.

      For this setup we need very little configuration in Azure. An Azure subscription with a storage account and Azure File Sync Service is all that we need. In the scenario described above all clients connect directly over SMB to the storage account. In this setup all users use SMB to connect to the file server and if a file is not local, the agent pulls the parts of the file that are needed over SSL to the server. If DFS-N is in the mix, it is also easy to migrate to new smaller disks while uploading the data to Azure to save space on your file server and storage. You can enable deduplication to further lower the storage footprint. Beware that files are unduplicated when they land in the storage account, so we cannot save space there.

      In this scenario user A accesses files from the IT folder in the DFS Share that are stored on the file server and delivered from local cache. The other file is from the marketing folder and not locally. The agent pulls the first bits to open the file to improve load time for the user while it continues to download the remaining bits. This way, Azure File Sync gives a performance advantage over the first scenario with Azure Files when working with big PDFs, PowerPoints or word documents when tiered files need to be downloaded from Azure Files.

      If your company is already using several resources in Azure and you might have an ExpressRoute connection, you can take advantage of syncing over Express Route instead of over the internet and use private endpoints to further lock down access.

      File server cluster with Azure File Sync

      In some cases, a company is more dependent on the files being available at all times and have an highly available (HA) file server. If you require an HA file server and currently have a cluster? No problem! The Azure File Sync agent is cluster aware. All we need is a second agent added to the scenario above with the single server. This way we can offload the data in the file server cluster to Azure File Shares.

      Multiple sites and regions use cases

      Most of the Azure resources and that include Azure Files are bound to their region for various reasons. For example underlying infrastructure reasons like network latency between resources. If your company operates on more geographical locations, it might not work to centralize files to a single place or a single region for Azure Files. In order to use multiple regions we need additional resources in the second region. US users accessing their files in Europe is less efficient because of the large distance. We can use Azure Files and Azure File Sync to offload data to Azure to overcome these challenges.

      Multi region with Azure Files

      In the example below we have offices in Europe and the US. The users can access their files through their locally available DFS Namespace and even access files from other locations. All files are pulled from Azure files to the user device for accessing and editing.

      Based on the setup, cross region traffic flows might be different. In the above example User C access a file in the Marketing US folder that is close to his office. User D access a file from the IT EU folder. The file from the Europe region is downloaded to his device and opened. Like in the first scenario all files come directly from the internet.

      Multi region with Azure File Sync

      As described in the scenario above with Azure Files, the setup with multiple locations is also possible with Azure File Sync. Users in both locations can access the files from their local file server and if the files are not available locally, the Azure File Sync agents pulls the bits from Azure Files transparently. When accessing files in the other region, like User C does, the same rules apply. If the file is locally available on the Europe file server, it’s presented directly to the user. If the file is not locally available, the agent of the file server in that region downloads the bits and provides it to the user so the file can be accessed.

      Move to Azure IaaS with Azure File Sync

      In some cases, companies move their file server to Azure IaaS. While the concept “Lift and Shift” looks plain and simple for file servers, it might not always be the answer because of disk efficiency, size and layout. Moving your file server 1-on-1 without optimizing it with cloud services can become a very cost inefficient solution. We have worked at projects with file servers containing 15TB of storage costing well over $2000 per month. When we optimized the fileserver with Azure File Sync, the costs dropped with more than 50%. The more storage, the bigger the savings.

      Pro-tip: Azure Backup

      Azure Backup is an Hybrid Backup solution on Microsoft Azure. With Azure Backup you are able to backup your VMs, SQL workloads and Files from your datacenter or hybrid datacenter. When using Azure Files and Azure File Sync you could leverage Azure Backup to further reduce datacenter storage costs and take advantage of the native integration of Azure Backup in Azure Files.

      In the case of Azure Files you may no longer have the option to backup the files in your datacenter. Well you technically could, it is probably not very efficient… With Azure Files sync you could do a file level backup of your file server but that would initiate a download of all the files and we don’t want that to happen.

      When going forward with a hybrid datacenter and moving files to the cloud, its important to also include the backup strategy in your design. When using Azure files it could be more cost efficient to use Azure Backup instead of you current backup solution.


      To wrap things up, we go back to our initial question. Can you still move files to the cloud if you can’t use Teams or SharePoint.. Yes you can!

      If you are looking at lowering the storage footprint or postpone a storage investment the above described scenarios might benefit you greatly. Start thinking about what an hybrid datacenter could do for you.

      Although it might seem straightforward, setups like this can be quite complicated and specific features might not work as you expect, backup is not as simple now and DR brings new options to the table. Based on the design there could also be hidden costs that are not as obvious as plain storage and/or license costs? At Splitbrain were a happy to help you out if you are looking at a hybrid datacenter with Azure Files and/or Azure File Sync, just drop us an e-mail!

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