Sizing infrastructure based on vendor Data Reduction assumptions – Part 1

One of the most common mistakes people make when designing solutions is making assumptions. Assumptions in short are things an architect has failed to investigate and/or validate which puts a project at risk of not delivering the desired business outcome/s.

A great example of a really bad assumption to make is what data reduction ratio a storage platform will deliver.

But what if a vendor offers a data reduction guarantee and promises to give you as much equipment required if the ratio is not achieved, you’re protected right? The risk of your assumption being wrong is mitigated with the promise of free storage. Hooray!

Let’s explore this for a minute using an example of one of the more ludicrous guarantees going around the industry at the moment:

A guarantee of 10:1 data reduction!

Let’s say we have 100TB of data, that means we’d only need 10TB right? This might only be say, 4RU of equipment which sounds great!

After deployment, we start migrating and we only get a more realistic 2:1 data reduction, at which point the project stalls due to lack of capacity.

I go back to the vendor and lets say, best case scenario they agree on the spot (HA!) to give you more equipment, its unlikely to be delivered in less than 4 weeks.

So your project is delayed a minimum of 4 weeks until the equipment arrives. You now need to go through your change control process and if you’re doing this properly it would be documented with detailed steps on how to install the equipment, including appropriate back out strategies in the event of issues.

Typically change control takes some time to prepare, go through approvals, documentation etc especially in larger mission critical environments.

When installing any equipment you should also have documented operational verification steps to ensure the equipment has been installed correctly and is highly available, performing as expected etc.

Now that the new equipment is installed, the project continues and all 100TB of your data has been migrated to the new platform. Hooray!

Now let’s talk about the ongoing implications of the assumption of 10:1 data reduction only resulting in a much more realistic 2:1 ratio.

We now have 5x more equipment than we expected, so assuming the original 10TB was 4RU, we would now have 20RU of equipment which is taking up valuable real estate in our datacenter, or which may have required you to lease another rack in your datacenter.

If the product you purchased was a SAN/NAS, you now have lower IOPS/GB as you have just added a bunch more disk shelves to the existing controllers. This is because the controllers have a finite amount of performance, and you’ve just added more drives for it to manage. More drives on a traditional two controller SAN/NAS is only a good thing if the controller is not maxed out, and with flash ever increasing in performance, Controllers will be assuming they are not already the bottleneck.

If the product was HCI, now you require considerably more network interfaces. Depending on the HCI platform, you may require more hypervisor licensing, further increasing CAPEX and OPEX.

Depending on the HCI product, can you even utilise the additional storage without changing the virtual machines configuration? It might sound silly but some products don’t distribute data throughout the cluster, rather having mirrored objects so you may even need to create more virtual disks or distribute the VMs to make use of the new capacity.

Then you need to consider if the HCI product has any scale limitations, as these may require you to redesign your solution.

What about operational expenses? We now have 5x more equipment, so our environmental costs such as power & cooling will increase significantly as will our maintenance windows where we now have to patch 5x more hypervisor nodes in the case of HCI.

Typically customers no longer size for 3-5 years due to the fact HCI is becoming the platform of choice compared to SAN/NAS. This is great but when your data reduction assumption is wrong, (in this example off by 5x) the ongoing impact is enormous.

This means as you scale, you need to scale at 5x the rate you originally designed for. That’s 5x more rack units (RU), 5x more Power, 5x more cooling required, potentially even 5x more hypervisor licensing.

What does all of this mean?

Your Total Cost of Ownership (TCO) and Return on Investment (ROI) goes out the window!

Interestingly, Nutanix recently considered offering a data reduction guarantee and I was one of many who objected and strongly recommended we not drop to the levels of other vendors just because it makes the sales cycle easier.

All of the reasons above and more were put to Nutanix product management and they made the right decision, even though Nutanix data reduction (and avoidance) is very strong, we did not want to put customers in a position where their business outcomes were potentially at risk due to assumptions.


While data reduction is a valuable part of a storage platform, the benefits (data reduction ratio) can and do vary significantly between customers and datasets. Making assumptions on data reduction ratios even when vendors provide lots of data showing their averages and providing guarantees, does not protect you from potentially serious problems if the data reduction ratios are not achieved.

In Part 2, I will go through an example of how misleading data reduction guarantees can be.

The truth about Storage Data efficiency ratios.

We’ve all heard the marketing claims from some storage vendors about how efficient their storage products are. Data efficiency ratios of 40:1 , 60:1 even 100:1 continue to be thrown around as if they are amazing, somehow unique or achieved as a result of proprietary hardware.

Let’s talk about how vendors may try to justify these crazy ratios:

For many years, Storage vendors have been able to take space efficient copies of LUNs, Datastores, Virtual Machines etc which rely on snapshots or metadata. These are not full copies and reporting this as data efficiency is quite mis-leading in my opinion as this is and has been for many years Table stakes.

Be wary of vendors encouraging (or requiring) you configure more frequent “backups” (which are after all just Snapshots or metadata copies) to achieve the advertised data efficiencies.

  • Reporting VAAI/VCAI clones as full copies

If I have a VMware Horizon View environment, It makes sense to use VAAI/VCAI space efficient clones as they provide numerous benefits including faster provisioning, recompose and use less space which leads to them being served from cache (making performance better).

So if I have an environment with just 100 desktops deployed via VCAI, You have a 100:1 data reduction ratio, 1000 desktops and you have 1000:1. But this is again Table stakes… well sort of because some vendors don’t support VAAI/VCAI and others only have partial support as I discuss in Not all VAAI-NAS storage solutions are created equal.

Funnily enough, one vendor even offloads what VAAI/VCAI can do (with almost no overhead I might add) to proprietary hardware. Either way, while VAAI/VCAI clones are fantastic and can add lots of value, claiming high data efficiency ratios as a result is again mis-leading especially if done so in the context of being a unique capability.

  • Compression of Highly compressible data

Some data, such as Logs or text files are highly compressible, so ratios of >10:1 for this type of data are not uncommon or unrealistic. However consider than if logs only use a few GB of storage, then 10:1 isn’t really saving you that much space (or money).

For example a 100:1 data reduction ratio of 100MB of logs is only saving you ~10GB which is good, but not exactly something to make a purchasing decision on.

Also compression of databases which lots of white space also compress very well, so the larger the Initial size of the DB, the more it will compress.

The compression technology used by storage vendors is not vastly different, which means for the same data, they will all achieve a similar reduction ratio. As much as I’d love to tell you Nutanix has much better ratios than Vendors X,Y and Z, its just not true, so I’m not going to lie to you and say otherwise.

  • Deduplication of Data which is deliberately duplicated

An example of this would be MS Exchange Database Availability Groups (DAGs). Exchange creates multiple copies of data across multiple physical or virtual servers to provide application and storage level availability.

Deduplication of this is not difficult, and can be achieved (if indeed you want to dedupe it) by any number of vendors.

In a distributed environment such as HCI, you wouldn’t want to deduplicate this data as it would force VMs across the cluster to remotely access more data over the network which is not what HCI is all about.

In a centralised SAN/NAS solution, deduplication makes more sense than for HCI, but still, when an application is creating the duplicate data deliberately, it may be a good idea to exclude it from being deduplicated.

As with compression, for the same data, most vendors will achieve a similar ratio so again this is table stakes no matter how each vendor tries to differentiate. Some vendors dedupe at more granular levels than others, but this provides diminishing returns and increased overheads, so more granular isn’t always going to deliver a better business outcome.

  • Claiming Thin Provisioning as data efficiency

If you have a Thin Provisioned 1TB virtual disk and you only write 50GB to the disk, you would have a data efficiency ratio of 20:1. So the larger you create your virtual disk and the less data you write to it, the better the ratio will be. Pretty silly in my opinion as Thin Provisioning is nothing new and this is just another deceptive way to artificially improve data efficiency ratios.

  • Claiming removal of zeros as data reduction

For example, if you create an Eager Zero Thick VMDK, then use only a fraction, as with the Thin Provisioning example (above), removal of zeros will obviously give a really high data reduction ratio.

However Intelegent storage doesn’t need Eager Zero Thick (EZT) VMDKs to give optimal performance nor will they write zeros to begin with. Intelligent storage will simply store metadata instead of a ton of worthless zeros. So a data reduction ratio from a more intelligent storage solution would be much lower than a vendor who has less intelligence and has to remove zeros. This is yet another reason why data efficiency (marketing) numbers have minimal value.

Two of the limited use cases for EZT VMDKs is Fault Tolerance (who uses that anyway) and Oracle RAC, so removal of zeros with intelligent storage is essentially moot.


Data reduction technologies have value, but they have been around for a number of years so if you compare two modern storage products, you are unlikely to see any significant difference between vendor A and B (or C,D,E,F and G).

The major advantage of data reduction is apparent when comparing new products with 5+ year old technology. If you are in this situation where you have very old tech, most newer products will give you a vast improvement, it’s not unique to just one vendor.

At the end of the day, there are numerous factors which influence what data efficiency ratio can be achieved by a storage product. When comparing between vendors, if done in a fair manner, the differences are unlikely to be significant enough to sway a purchasing decision as most modern storage platforms have more than adequate data reduction capabilities.

Beware: Dishonest and mis-leading marketing about data reduction is common so don’t get caught up in a long winded conversations about data efficiency or be tricked into thinking one vendor is amazing and unique in this area, it just isn’t the case.

Data reduction is table stakes and really shouldn’t be the focus of a storage or HCI purchasing decision.

My recommendation is focus on areas which deliver operational simplicity, removes complexity/dependancies within the datacenter and achieve real business outcomes.

Nutanix Implementation of Data Avoidance & Reduction Technologies

While its not news that Nutanix Distributed Storage Fabric (NDSF) supports numerous data avoidance & reduction technologies, what is less well known is how these technologies can be enabled/disabled and used.

Before we begin, let me cover off what technologies NDSF offers:

Data Avoidance:

  • VAAI-NAS Fast File Clone (for ESXi)
  • View Composer for Array Integration (VCAI) for Horizon View
  • Native NDSF Clones (ESXi, Hyper-V and AHV)
  • ODX Copy Offload (Hyper-V)
  • Crash and Application Consistent snapshots (ESXi, Hyper-V and AHV)

Data Reduction:

  • Compression (In-Line and Post-Process)
  • Deduplication (Fingerprint on Write/In-Line for Performance Tier and/or Capacity Tier)
  • Erasure Coding (EC-X)

Data avoidance is designed to prevent the creation of unnecessary data which removes the requirement to leverage data reduction technologies. This means less work for the storage layer which results in more available front end IO to service the virtual machines.

An example of data avoidance is using VCAI with Horizon View to create Linked Clones near instantly which not only reduces space but ensures faster deployment and recompose activities with greatly reduced impact to the environment.

Data avoidance is greatly underrated in my opinion, as it results in lower compression/deduplication ratios, because there is no additional data to dedupe or compress. If Nutanix turned off these data avoidance technologies, it would result in HIGHER compression and dedupe ratios, which sounds great on a marketing slide or in a tweet, but in reality, avoiding work for the storage is a much better way to do things.

Some vendors report data avoidance such as snapshots in deduplication ratios, and this in my opinion is very misleading and designed to artifically inflate dedupe ratios for competitive purposes. For more information see: Deduplication ratios – What should be included in the reported ratio?

Data Reduction is still a valuable option to have but in my opinion its overrated. The reason I think its overrated is data reduction does not always work well. It greatly depends on your data type if you will see a good data reduction ratio or not, AND if the overheads (of which there is always an overhead) are worth it.

Let’s now focus on the NDSF implementation of Data Reduction technologies.


Compression can be configured on new or existing containers and be set to In-Line or Post-Process. For post process, enter a “Delay” value e.g.: 60 to delay compression for 1 Hour, or 3600 for 1 day.


Compression can be reconfigured at any time, without the requirement to relocate VMs or reformat the storage. For data which is already compressed it will be uncompressed as part of a low priority background task (known as Curator). This ensures there is low/no impact of changing Compression settings, ensuring maximum flexibility for customers.

Because compression is configured per container, you can have VMs or even Virtual Disks running compression alongside VMs or Virtual Disks not running compression within the same NDSF cluster. This helps eliminate silos and ensures mixed workloads with different data types/profiles can co-exist efficiently.


As with Compression, Deduplication can be configured on new or existing containers and be set to dedupe for the performance tier (SSD) and optionally for the Capacity (HDD) Tier. This means data reduction can be maximised for either or both tiers depending on customer requirements.


Again the same as Compression, Dedupe can be reconfigured at any time, without the requirement to relocate VMs or reformat the storage. For data which is already deduped the same low priority background task (Curator) rehydrates the data again ensuring there is low/no impact of changing dedupe settings and ensuring maximum flexibility for customers.

Because dedupe is configured per container, you can have VMs or even Virtual Disks running dedupe alongside VMs or Virtual Disks not running dedupe within the same NDSF cluster. Deduplication is also complimentary to Compression, meaning both can be ran at the same time to maximise data reduction and further eliminate silos ensuring mixed workloads can co-exist efficiently.

Erasure Coding (EC-X):

As with Compression & Dedupe, EC-X is enabled on a per container basis and is complimentary to both Compression and Dedupe. EC-X is a post-process only form of data reduction designed to work on Write cold data (meaning data which is not changing).

EC-X applies to data across the Performance Tier (SSD) and the Capacity Tier (SATA) which means the effective SSD capacity is increased, which means more data can be serviced by SSD, thus increasing performance.


As previously discussed, NDSF supports different containers using different combinations of data reduction all within the same NDSF cluster to maximise efficiencies and eliminate unnecessary silos.


Nutanix provides multiple technologies to minimise the data being stored on the distributed storage fabric while giving customers the flexibility to enable/disable and tune data reduction settings to suit different data profiles all within the same NDSF cluster.

Remember, “one size does not fit all” so it is importaint for the storage layer to be able treat your workloads differently based on their individual requirements.

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