Category Archives: Storage

How to Architect a VSA , Nutanix or VSAN solution for >=N+1 availability.

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How to architect a VSA, Nutanix or VSAN solution for the desired level of availability (i.e.: N+1 , N+2 etc) is a question I am asked regularly by customers and contacts throughout the industry.

This needs to be addressed in two parts.

1. Compute
2. Storage

Firstly, Compute level resiliency, As a cluster grows, the chances of a failure increases so the percentage of resources reserved for HA should increase with the size of the cluster.

My rule of thumb (which is quite conservative) is as follows:

1. N+1 for clusters of up to 8 hosts
2. N+2 for clusters of >8 hosts but <=16
3. N+3 for clusters of >16 hosts but <=24
4. N+4 for clusters of >24 hosts but <=32

The above is discussed in more detail in : Example Architectural Decision – High Availability Admission Control Setting and Policy

The below table highlights in Green my recommended HA percentage configuration based on the cluster size, up to the current vSphere limit of 32 nodes.

HApercentages

Some of you may be thinking, if my Nutanix or VSAN cluster is only configured for RF2 or FT1 for VSAN, I can only tolerate one node failure, so why am I reserving more than N+1.

In the case of Nutanix, after a node failure, the cluster can restore itself to a fully resilient state and tolerate subsequent failures. In fact, with “Block Awareness” a full 4 node block can be lost (so an N-4 situation) which if this is a requirement, needs to be considered for HA admission control reservations to ensure compute level resources are available to restart VMs.

Next lets talk about the issue perceived to be more complicated, Storage redundancy.

Storage redundancy for VSA, Nutanix or VSAN is actually not as complicated as most people think.

The following is my rule of thumb for sizing.

For N+1 , Ensure you have enough capacity remaining in the cluster to tolerate the largest node failing.

For N+2, Ensure you have enough capacity remaining in the cluster to tolerate the largest TWO nodes failing.

The examples below discuss Nutanix nodes and their capacity, but the same is applicable to any VSA or VSAN solution where multiple copies of data is kept for data protection, as opposed to RAID.

Example 1 , If you have 4 x Nutanix NX3060 nodes configured with RF2 (FT1 in VSAN terms) with 2TB usable per node (as shown below), in the event of a node failure, 2TB is no longer available. So the maximum storage utilization of the cluster should be <75% (6TB) to ensure in the event of any node failure, the cluster can be restored to a fully resilient state.

4node3060

Example 2 , If you have 2 x Nutanix NX3060 nodes configured with RF2 (FT1 in VSAN terms) with 2TB usable per node and 2 x Nutanix NX6060 nodes with 8TB usable per node (as shown below), in the event of a NX6060 node failure, 8TB is no longer available. So the maximum storage utilization of the cluster should be 12TB to ensure in the event of any node failure (including the 8TB nodes), the cluster can be restored to a fully resilient state.

4nodemixed

For environments using Nutanix RF3 (3 copies of data) or VSAN (FT2) the same rule of thumb applies but the usable capacity per node would be lower due to the increased capacity required for data protection.

Specifically for Nutanix environments, the PRISM UI shows if a cluster has sufficient capacity available to tolerate a node failure, and if not the following is displayed on the HOME screen and alerts can be sent if desired.

CapacityCritical

In this case, the cluster has suffered a node failure, and because it was sized suitably, it shows “Rebuild Capacity Available” as “Yes” and advises an “Auto Rebuild in progress” meaning the cluster is performing a fully automated self heal. Importantly no admin intervention is required!

If the cluster status is normal, the following will be shown in PRISM.

CapacityOK

In summary: The smaller the cluster the higher the amount of capacity needs to remain unused to enable resiliency to be restored in the event of a node failure, the same as the percentage of resources reserved for HA in a traditional compute only cluster.

The larger the cluster from both a storage and compute perspective, the lower the unused capacity is required for HA, so as has been a virtualization recommended practice for years….. Scale-out!

Related Articles:

1. Scale Out Shared Nothing Architecture Resiliency by Nutanix

2. PART 1 – Problems with RAID and Object Based Storage for data protection

3. PART 2 – Problems with RAID and Object Based Storage for data protection

Microsoft Exchange on Nutanix Best Practice Guide

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I am pleased to announce that the Best Practice guide for Microsoft Exchange on Nutanix is released and can be found here.

For me deploying MS Exchange on Nutanix with vSphere combines best of breed application level resiliency (in the form of Exchange Database Availability Groups), infrastructure and hypervisor technologies to provide an infrastructure with not only high performance, but with industry leading scalability, no silos and very high efficiency & resiliency.

All of this leads to overall lower CAPEX/OPEX for customers.

In summary by Virtualizing MS Exchange on Nutanix, customers realize several key benefits including:

  • Ability to use a standard platform for all workloads in the datacenter, thus allowing the removal of legacy silos resulting in lower overall cost, and increased operational efficiencies.
    • An example of this is no disruption to MS Exchange users when performing Nutanix / Hypervisor or HW maintenance
  • A highly resilient , scalable and flexible MS Exchange deployment.
  • Reducing the number of Exchange Mailbox servers required to maintain 4 copies of Exchange data thanks to the combination of NDFS + DAG. (2 copies at NDFS layer / 2 copies at DAG layer)
  • Eliminate the need for large / costly refresh cycles of HW as individual nodes can be added and removed non disruptively.
  • Simplified architecture, no need for complex sizing architecture or risk of over sizing day 1, start small and scale VMs, Compute or storage if/when required.
  • No dependency of specific HW, Exchange VMs can be migrated to/from any Nutanix node and even to non Nutanix nodes.
  • Full support from Nutanix including at the Exchange, Hypervisor and Storage layers with support from Microsoft via Premier Support contracts or via TSANet.
  • Lower CAPEX/OPEX as Exchange can be combined with new or existing Nutanix/Virtualization deployment.
  • Reduced datacenter costs including Power, Cooling , Space (RU)

I hope you enjoy the Best Practice guide and look forward to hearing about your MS Exchange on Nutanix questions & experiences.

Rule of Thumb: Sizing for Storage Performance in the new world.

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In the new world where storage performance is decoupled with capacity with new read/write caching and Hyper-Converged solutions, I always get asked:

How do I size the caching or Hyper-Converged solution to ensure I get the storage performance I need.

Obviously I work for Nutanix, so this question comes from prospective or existing Nutanix customers, but its also relevant to other products in the market, such as PernixData or any Hybrid (SSD+SAS/SATA) solution.

So for indicative sizing (i.e.: Presales) where definitive information is not available and/or where you cannot conduct a detailed assessment , I use the following simple Rule of Thumb.

Take your last two monthly full backups, and take the delta between them and multiply that by 3.

So if my full backup from August was 10TB and my full backups from September is 11TB, my delta is 1TB. I then multiply that by 3 and we get 3TB which is our assumption of the “Active Working Set” or in basic terms, the data which needs performance. (Because cold or inactive data can sit on any tier without causing performance issues).

Now I  size my SSD tier for 3TB of usable capacity.

The next question is:

Why multiple the backup data delta by 3?

This is based on an assumption (since we don’t have any hard data to go on) that the Read/Write ratio is 70% Read, 30% write.

Now those of you familiar with this thing called Maths, would argue 70/30 is 2.33333 which is true. So rounding up to 3 is essentially a buffer.

I have found this rule of thumb works very well, and customers I have worked with have effectively had All Flash Array performance because the “Active Working Set” all resides within the SSD tier.

Caveats to this rule of thumb.

1. If a customer does a significant amount of deletions during the month, the delta may be smaller and result in an undersized SSD tier.

Mitigation: Review several months of full backup logs and average the delta.

2. If the environment’s Read/Write ratio is much higher than 70/30, then the delta from the backup multiplied by 3 may again result in  an undersized SSD tier.

Mitigation: Perform some investigation into your most critical workloads and validate or correct the assumption of multiplying by 3

3. This rule of thumb is for Server workloads, not VDI.

VDI Read/Write ratio is generally almost opposite to server, and around 30/70 Read/Write. However the SSD tier for VDI should be sized taking into account the benefits of VAAI/VCAI cloning and things like de duplication (for Memory and SSD tiers) which some products, like Nutanix offer.

Summary / Disclaimer

This rule of thumb works for me 90% of the time when designing Nutanix solutions, but your results may vary depending on the platform you use.

I welcome any feedback or suggestions of alternate sizing strategies which I will update the post with where appropriate.