Expanding Capacity on a Nutanix environment – Design Decisions

I recently saw an article about design decisions around expanding capacity for a HCI platform which went through the various considerations and made some recommendations on how to proceed in different situations.

While reading the article, it really made me think how much simpler this process is with Nutanix and how these types of areas are commonly overlooked when choosing a platform.

Let’s start with a few basics:

The Nutanix Acropolis Distributed Storage Fabric (ADSF) is made up of all the drives (SSD/SAS/SATA etc) in all nodes in the cluster. Data is written locally where the VM performing the write resides and replica’s are distributed based on numerous factors throughout the cluster. i.e.: No Pairing, HA pairs, preferred nodes etc.

In the event of a drive failure, regardless of what drive (SSD,SAS,SATA) fails, only that drive is impacted, not a disk group or RAID pack.

This is key as it limited the impact of the failure.

It is importaint to note, ADSF does not store large objects nor does the file system require tuning to stripe data across multiple drives/nodes. ADSF by default distributes the data (at a 1MB granularity) in the most efficient manner throughout the cluster while maintaining the hottest data locally to ensure the lowest overheads and highest performance read I/O.

Let’s go through a few scenarios, which apply to both All Flash and Hybrid environments.

  1. Expanding capacityWhen adding a node or nodes to an existing cluster, without moving any VMs, changing any configuration or making any design decisions, ADSF will proactively send replicas from write I/O to all nodes within the cluster, therefore improving performance while reactively performing disk balancing where a significant imbalance exists within a cluster.

    This might sound odd but with other HCI products new nodes are not used unless you change the stripe configuration or create new objects e.g.: VMDKs which means you can have lots of spare capacity in your cluster, but still experience an out of space condition.

    This is a great example of why ADSF has a major advantage especially when considering environments with large IO and/or capacity requirements.

    The node addition process only requires the administrator to enter the IP addresses and its basically a one click, capacity is available immediately and there is no mass movement of data. There is also no need to move data off and recreate disk groups or similar as these legacy concepts & complexities do not exist in ADSF.

    Nutanix is also the only platform to allow expanding of capacity via Storage Only nodes and supports VMs which have larger capacity requirements than a single node can provide. Both are supported out of the box with zero configuration required.

    Interestingly, adding storage only nodes also increases performance, resiliency for the entire cluster as well as the management stack including PRISM.

  2. Impact & implications to data reduction of adding new nodesWith ADSF, there are no considerations or implications. Data reduction is truely global throughout the cluster and regardless of hypervisor or if you’re adding Compute+Storage or Storage Only nodes, the benefits particularly of deduplication continue to benefit the environment.

    The net effect of adding more nodes is better performance, higher resiliency, faster rebuilds from drive/node failures and again with global deduplication, a higher chance of duplicate data being found and not stored unnecessarily on physical storage resulting in a better deduplication ratio.

    No matter what size node/s are added & no matter what Hypervisor, the benefits from data reduction features such as deduplication and compression work at a global level.

    What about Erasure Coding? Nutanix EC-X creates the most efficient stripe based on the cluster size, so if you start with a small 4 node cluster your stripe would be 2+1 and if you expand the cluster to 5 nodes, the stripe will automatically become 3+1 and if you expand further to 6 nodes or more, the stripe will become 4+1 which is currently the largest stripe supported.

  3. Drive FailuresIn the event of a drive failure (SSD/SAS or SATA) as mentioned earlier, only that drive is impacted. Therefore to restore resiliency, only the data on that drive needs to be repaired as opposed to something like an entire disk group being marked as offline.

    It’s crazy to think a single commodity drive failure in a HCI product could bring down an entire group of drives, causing a significant impact to the environment.

    With Nutanix, a rebuild is performed in a distributed manner throughout all nodes in the cluster, so the larger the cluster, the lower the per node impact and the faster the configured resiliency factor is restored to a fully resilient state.

At this point you’re probably asking, Are there any decisions to make?

When adding any node, compute+storage or storage only, ensure you consider what the impact of a failure of that node will be.

For example, if you add one 15TB storage only node to a cluster of nodes which are only 2TB usable, then you would need to ensure 15TB of available space to allow the cluster to fully self heal from the loss of the 15TB node. As such, I recommend ensuring your N+1 (or N+2) node/s are equal to the size of the largest node in the cluster from both a capacity, performance and CPU/RAM perspective.

So if your biggest node is an NX-8150 with 44c / 512GB RAM and 20TB usable, you should have an N+1 node of the same size to cover the worst case failure scenario of an NX-8150 failing OR have the equivalent available resources available within the cluster.

By following this one, simple rule, your cluster will always be able to fully self heal in the event of a failure and VMs will failover and be able to perform at comparable levels to before the failure.

Simple as that! No RAID, Disk group, deduplication, compression, failure, or rebuild considerations to worry about.


The above are just a few examples of the advantages the Nutanix ADSF provides compared to other HCI products. The operational and architectural complexity of other products can lead to additional risk, inefficient use of infrastructure, misconfiguration and ultimately an environment which does not deliver the business outcome it was originally design to.

Why Nutanix Acropolis hypervisor (AHV) is the next generation hypervisor – Part 10 – Cost

You may be surprised cost is so far down the list but as you have probably realized by reading the previous 9 parts is that AHV is in many ways a superior virtualization platform to other products on the market. In my opinion, it would be a mistake to think AHV is a “low-cost option” or “a commodity hypervisor with limited capabilities” just because it happens to be included with Starter Edition (making it effectively free for all Nutanix customers).

Apart from the obvious removal of hypervisor and associated management component licensing/ELA costs, the real cost advantage of using AHV is the dramatic reduction in effort required in the design, implementation, operational verification phases as well as ongoing management.

This is due to many factors:

Simplified Design Phase

As all AHV Management components are in-built, highly available and auto scaling, there is no need to engage a Subject Matter Expert (SME) to design the management solution. As a person who has designed countless highly available virtualization solutions over the years, I can tell you AHV out of the box is what I have all but dreamed of creating with other products for customers in the past.

Simplified Implementation Phase

All management components (with the exception of Prism Central) are deployed automatically removing the requirement for an engineer to install/patch/harden these components.

Building Acropolis and all management components into the CVM means there are fewer moving parts that can go wrong and therefore that need to be verified.

In my experience, Operational Verification is one of the areas regularly overlooked and infrastructure is put into production without having proven it meets the design requirements and outcomes. With AHV management components deployed automatically, the risk of components not delivering is all but eliminated and where Operational Verification is performed, it can be completed much faster than traditional products due to having much fewer moving parts.

Simplified ongoing operations

Acropolis provides One-Click fully automated rolling upgrades for Acropolis Base Software (formally known as NOS), Acropolis Hypervisor, Firmware and Nutanix Cluster Check (NCC). In addition, upgrades can be automatically downloaded removing the risk of installing incompatible versions and the requirement to check things such as Hardware Compatability Lists (HCLs) and interoperability matrix’ before upgrades.

AHV dramatically simplifies Capacity management by only requiring capacity management to be done at the Storage Pool layer; there is no requirement for administrators to manage capacity between LUNs/NFS mounts or Containers. This capability also eliminates the requirement for well-known hypervisor features such as vSphere’s Storage DRS.

Reduced 3rd party licensing costs

AHV includes all management components, or in the case of Prism Central, come as a prepackaged appliance. There is no need to license any operating systems. The highly resilient management components on every Nutanix node eliminates the requirement for 3rd party database products such as Microsoft SQL or Oracle or best case scenario, the deployment of Virtual Appliances which may not be highly available and which needs to be backed up and maintained.

Reduced Management infrastructure costs

It is not uncommon for virtualization solutions to require a dozen or more management components (each potentially on a dedicated VM) even for small deployments to get all the functionality such as centralized management, patching and performance/capacity management. As deployments grow or have higher availability requirements, the number of management VMs and their compute requirements tend to increase.

As all management components run within the Nutanix Controller VM (CVM) which resides on each Nutanix node, there is no need to have a dedicated management cluster. The amount of compute/storage resources are also reduced.

The indirect cost savings for the reduced management infrastructure include:

  1. Less rack space (RU)
  2. Less power/cooling
  3. Fewer network ports
  4. Less compute nodes
  5. Lower storage capacity & performance requirements

Last but not least, what about the costs associated with maintenance windows or outages?

Because Acropolis provides fully non-disruptive one-click upgrades and removes numerous points of failure (e.g.: 3rd Party Databases) while providing an extremely resilient platform, AHV also reduces the cost to the customer of maintenance and outages.


  1. No design required for Acropolis management components
  2. No ongoing maintenance required for management components
  3. Reduced complexity reduces the chance of downtime as a result of human error

Back to the Index

Things to consider when choosing infrastructure.

With all the choice in the compute/storage market at the moment, choosing new infrastructure for your next project is not an easy task.

In my experience most customers (and many architects) think about the infrastructure coming up for replacement and look to do a “like for like” replacement with newer/faster technology.

An example of this would be a customer with a FC SAN running Oracle workloads where the customer or architect replaces the end of life Hybrid FC SAN with an All Flash FC SAN and continues running Oracle “as-is”.

Now I’m not saying there is anything wrong with that, however if we consider more than just the one workload, we may be able to achieve our business requirements with a more standardized and cost effective approach than having dedicated infrastructure for specific workloads.

So in this post, I am inviting you to consider the bigger picture.

If we take an example customer has the following workload requirements:

  1. Virtual Desktop (VDI)
  2. Virtualized Business Critical Applications (e.g.: SQL / Exchange)
  3. Long Term Archive (High Capacity, low IOPS)
  4. Business Continuity and Disaster Recovery

It is unlikely any one solution from any vendor is going to be the “best” in all areas as every solution has its pros and cons.

Regarding VDI, I would say most people would agree Hyperconverged Infrastructure (HCI) / Scale out type architectures are strong for VDI, however VDI can be successfully deployed on a traditional SAN/NAS solutions or using non shared local storage in the case of non-persistent desktops.

For vBCA, some people believe physical servers with JBOD storage is best for workloads like Exchange, and Physical + local SSD are best for Databases while many people are realising the benefits of virtualization of vBCA with shared storage such as SAN/NAS or on HCI.

For long term archive, cost per GB is generally one of if not the most critical factor where lots of trays of SATA storage connected to a small dual controller setup may be the most cost effective, whereas an All Flash array would be less likely considered in this use case.

For BC/DR, features such as a Storage Replication Adapter (SRA) for VMware Site Recovery Manager, a stretched cluster capability and some form of snapshot capability and replication would be typical requirements. Some newer technology can do per VM snapshots, whereas older style SAN/NAS technology may be per LUN, so newer technology would have an advantage here, but again, this doesn’t mean one tech should not be considered.

So what product do we choose for each workload type? The best of breed right?

Well, maybe not. Lets have a look at why you might not want to do that.

The below graph shows an example of 3 vendors being compared across the 4 categories I mentioned above being VDI, vBCA, Long Term Archive and BC/DR.


The customer has determined that a score of 3 is required to meet their requirements so a solution failing to achieve a 3 or higher will not be considered (at least for that workload).

As we can see, for VDI Vendor B is the strongest, Vendor A second and Vendor C third, but when we compare BC/DR Vendor C is strongest followed by Vendor A and lastly Vendor B.

We can see for Long Term Archive Vendor A is the strongest with Vendor B and C tied for second place and finally for vBCA Vendor B is the strongest, Vendor A second and Vendor C third.

So if we chose the best vendor for each workload type (or the “Best of breed” solution) we would end up with three different vendors equipment.

  • VDI: Vendor B
  • Long Term Archive: Vendor A
  • BC/DR: Vendor C
  • vBCA: Vendor B

Is this a problem? Not necessarily but I would suggest that there are several things to consider including:

1. Having 3 different platforms to design/install/maintain

This means 3 different sets of requirements, constraints, risks, implications need to be considered.

Some large organisations may not consider this a problem, because they have a team for each area, but isn’t the fact the customer has to have multiple teams to manage infrastructure a problem in itself? Sounds like a significant (and potentially unnecessary) OPEX to me.

2. The best BC/DR solution does not meet the minimum requirements for the vBCA workloads.

In this example, the best BC/DR solution (Vendor C) is also the lowest rated for vBCA. As a result, Vendor C is not suitable for vBCA which means it should not be considered for BC/DR of vBCA. If Vendor C was used for BC/DR of the other workloads, then another product would need to be used for vBCA adding further cost/complexity to the environment.

3. Vendor A is the strongest at Long Term Archive, but has no interoperability with Vendor B and C

Due to the lack of interoperability, while Vendor A has the strongest Archiving solution, it is not suitable for this environment. In this example, the difference between the strongest Long Term Archive solution and the weakest is very small so Vendor B and C also meet the customers requirements.

 4. Multiple Silos of infrastructure may lead to inefficient use.

Just like in the days before Virtualization, we had the bulk of our servers CPU/RAM running at low utilization levels, we had our storage capacity carved up where we had lots of free space in one RAID pack but very little free space in others and we spent lots of time migrating workloads from LUN 1 to LUN 2 to free up capacity for new or existing workloads.

If we have 3 solutions, we may have many TB of available capacity in the VDI environment but be unable to share it with the Long Term Archiving. Or we may have lots of spare compute in VDI and be unable to share it with vBCA.

Now getting back to the graph, the below is the raw data.


What we can see is:

  • Vendor B has the highest total (17.1)
  • Vendor A has the second highest total (14.8)
  • Vendor C has the lowest total (12)
  • Vendor C failed to meet the minimum requirements for VDI & vBCA
  • Vendor A and B met the minimum requirements for all areas

Let’s consider the impact of choosing Vendor B for all 4 workload types.

VDI – It was the highest rated, met the minimum requirements for the customer and is best of breed, so in this case Vendor B would be a solid choice.

vBCA – Again Vendor B was the highest rated, met the minimum requirements for the customer and is best of breed, so Vendor B would be a solid choice.

Long Term Archiving: Vendor B was equal last, but importantly met the customer requirements. Vendor A’s solution may have more features and higher performance, but as Vendor B met the requirements, the additional features and/or performance of Vendor A are not required. The difference between Vendor A (Best of Breed) and Vendor B was also minimal (0.5 rating difference) so Vendor B is again a solid choice.

BC/DR: Vendor B was the lowest rated solution for BC/DR, but again focusing on the customers requirements, the solution exceeded the minimum requirement of 3 comfortably with a rating of 4.2. Choosing Vendor B meets the requirements and likely avoids any interoperability and/or support issues, meaning a simpler overall solution.

Let’s think about some of the advantages for a customer choosing a standard platform for all workloads in the event a platform meets all requirements.

1. Lower Risk

Having a standard platform minimizes the chance of interoperability and support issues.

2. Eliminating Silos

As long as you can ensure performance meets requirements for all workloads (which can be difficult on centralized SAN/NAS deployments) then using a standard platform will likely lead to better utilization and higher return on investment (ROI).

3. Reduced complexity / Single Pane of Glass Management

Having one platform means not having to have SMEs in multiple technologies, or in larger organisations multiple SMEs per technology (for redundancy and/or workload) meaning reduced complexity, lower operational costs and possibly centralized management.

4. Lower CAPEX

This will largely depend on the vendor and quantity of infrastructure purchased, however many customers I have worked with have excellent pricing from a vendor as a result of standardizing.


I am in no way saying “One size fits all” or that “every problem is a Nail” and recommending you buy a hammer. What I am saying is when considering infrastructure for your environment (or your customers), avoid tunnel vision and consider the other workloads or existing infrastructure in the environment.

In many cases the “Best of Breed” solution is not required and in fact implementing that solution may have significant implications in other areas of the environment.

In other cases, workloads may be so mission critical, that a best of breed solution may be the only way to meet the business requirements, in which case, a using a standard platform that may not meet the requirements would not be advised.

However if you can meet all the customer requirements with a standard platform while working within constraints such as budget, power, cooling, rack space and time to value, then I would suggest your doing yourself (or your customer) a dis-service by not considering using a standard platform for your workloads.

Related Articles:

1. Enterprise Architecture & Avoiding tunnel vision.

2. Peak Performance vs Real World Performance