Tag Archives: vmware

Example Architectural Decision – Transparent Page Sharing (TPS) Configuration for VDI (1 of 2)

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Problem Statement

In a VMware vSphere environment, with future releases of ESXi disabling Transparent Page Sharing by default, what is the most suitable TPS configuration for a Virtual Desktop environment?

Assumptions

1. TPS is disabled by default
2. Storage is expensive
3. Two Socket ESXi Hosts have been chosen to align with a scale out methodology.
4. HA Admission Control policy used is “Percentage of Cluster Resources reserved for HA”
5. vSphere 5.5 or earlier

Requirements

1. VDI environment must deliver consistent performance
2. VDI environment supports a high percentage of Power Users

Motivation

1. Reduce complexity where possible.
2. Maximize the efficiency of the infrastructure

Architectural Decision

Leave TPS disabled (default) and apply 100% Memory Reservations to VDI VMs and/or Golden Master Image.

Justification

1. Setting 100% memory reservations ensures consistent performance by eliminating the possibility of swapping.
2. The 100% memory reservation also eliminates the capacity usage by the vswap file which saves space on the shared storage as well as reducing the impact on the storage in the event of swapping.
3. RAM is cheaper than Tier 1 storage (which is recommended for vSwap storage to ensure minimal performance impact during swapping) so the increased cost of memory in the hosts is easily offset by the saving in shared storage.
4. Simplicity. Leaving default settings is advantageous from both an architectural and operational perspective.  Example: ESXi Patching can cause settings to revert to default which could negate TPS savings and put a sudden high demand on storage where TPS savings are expected.
5. TPS savings for desktops can be significant, however with a high percentage of Power Users with >=4GB desktops and 2vCPUs, the TPS savings are lower compared to Kiosk or Task users typically with 1-2GB per desktop.
6. The decision has been made to use 2 socket ESXi hosts and scale out so the TPS savings per host compared to a 4 socket server with double the RAM will be lower.
7. HA admission control will calculate fail-over requirements (when using Percentage of cluster resources reserved for HA) so that performance will be approximately the same in the event of a fail-over due to reserving the full RAM reserved for every VM leading to more consistent performance under a wider range of circumstances.
8. Lower core count (and lower cost) CPUs will likely be viable as RAM will likely be the first constraint for further consolidation.

Implications

1. Using 100% memory reservations requires ESXi hosts and the cluster be sized at a 1:1 ratio of vRAM to pRAM (Physical RAM) and should include N+1 so a host failure can be tolerated.
2. Increased RAM costs
3. No memory overcommitment can be achieved
4. Potential for lower CPU utilization / overcommitment as RAM may become the first constraint.

Alternatives

1. Use 50% reservation and enable TPS
2. Use no reservation, Enable TPS and disable large pages

Related Articles:

1. The Impact of Transparent Page Sharing (TPS) being disabled by default @josh_odgers (VCDX#90)

2. Example Architectural Decision – Transparent Page Sharing (TPS) Configuration for VDI (2 of 2)

3. Future direction of disabling TPS by default and its impact on capacity planning –@FrankDenneman (VCDX #29)

4. Transparent Page Sharing Vulnerable, Yet Largely Irrelevant – @ChrisWahl(VCDX#104)

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

Cost vs Reward for the Nutanix Controller VM (CVM)

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I hear a lot of FUD (Fear Uncertainty and Doubt) getting thrown around about the Nutanix Controller VM (CVM) being a resource (vCPU/vRAM) hog.

So I thought I would address this perceived issue.

For those of you who are car people, you will understand the benefits of a Supercharger increasing performance of an engine.

The supercharger does this by attaching a belt to a pulley connected to the motor which spins the supercharger to force more air into the combustion chambers. This allows more fuel to be added to the mix to produce higher horsepower from the same engine displacement (engine capacity, ie: 2.0 Litres)

What is downside of a Supercharger?

The supercharger belt connected to the pulley can require even hundreds of horsepower to simply drive the supercharger. As such, a 300HP engine may have to use half of its power to just drive the supercharger.

So for example, a 300HP engine less 60HP (25%) to drive the supercharger equates to only 240HP remaining. But, as a result of the supercharger forcing more air into the engine, the engine now produces an additional 200HP.

So the “cost” of running the supercharger is 60HP, but the overall benefit is 200HP, resulting in the engine now producing 440HP.

Let’s now relate this back to the Nutanix Controller VM (CVM).

The CVM provides the storage features,functionality,excellent scalability and performance for the Virtual Machines. For example, reducing the latency thanks to Data Locality keeping data local to the compute node running the VM for faster reads and writes.

The faster the reads and writes, the less time VMs spend in a “CPU wait” state waiting for I/Os to be acknowledged by the storage which means the CPUs are being more efficiently utilized. This is a small part of the value the Nutanix CVM provides.

In Summary, the CVM does use some compute resources from the host (which depend on the node type and performance required) but like a Supercharger to an engine, the Nutanix CVM delivers significantly higher value to the VMs than the resources it uses.

Related Articles:

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

2. Is VAAI beneficial with Virtual Storage Appliance (VSA) based solutions ?

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