Tag Archives: cluster

Example Architectural Decision – Hyperthreading with Business Critical Applications (Exchange 2013)

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Problem Statement

When Virtualizing Exchange 2013 (which is considered by the customer as a Business Critical Application) in a vSphere cluster shared with other production workloads of varying sizes and performance requirements,  should Hyper Threading (HT) be used?

Assumptions

1. vSphere 5.0 or greater
2. Exchange Servers are correctly sized day one or are subsequently “Right Sized”
3. Cluster average CPU overcommitment of 3:1

Motivation

1. Ensure Optimal performance for BCAs (Exchange)
2. Ensure Optimal performance for other Virtual servers in the shared vSphere cluster

Architectural Decision

Enable Hyper Threading (HT)

Alternatives

1. Disable Hyper Threading (HT)
2. Enable Hyper Threading but configure Exchange Virtual machine/s with Advanced CPU, HT Sharing Mode of “None” to ensure Exchange is always scheduled onto physical CPU cores
3. Split off a limited number of ESXi hosts and form a dedicated BCA cluster w/ <= 2:1 overcommitment and disable HT
4. Disable HT on a number of nodes within the cluster but leave HT enabled on other nodes and use DRS rules to pin Exchange VMs to non HT hosts

Justification

1. Enabling Hyper Threading (HT) improves the efficiency of the CPU scheduler, which will minimize the possibility of CPU Ready for the Exchange server/s and other virtual machines on the host where a low level of overcommitment exists (<2:1)
2. For optimal performance, DRS “Should” rules will be used to keep Exchange (BCA) workloads on specific ESXi hosts within the cluster where <=2:1 CPU overcommitment is maintained
3. Configuring Advanced CPU, HT Sharing Mode to “None” (to guarantee only pCore’s are used) may result in increased CPU Ready as the CPU scheduler is forced to find (and wait) for available pCore’s which may result in degraded or inconsistent performance.
4. Sizing for the Exchange solution was completed taking into account only pCore’s (Not HT cores) to simplify sizing
5. As the cluster where Exchange is virtualized is shared with other server workloads with varying levels of importance and performance, HT benefits the vast majority of workloads and results in a higher consolidation ratio and better performance for the vSphere cluster as a whole.
6. In physical servers, enabling Hyper Threading on Exchange servers resulted in wasted or excessive RAM usage for .NET garbage collection due to memory for .NET being allocated based on logical cores. This does not impact “Right Sized” Virtual Machines as only the required number of vCPUs are assigned to the VM, and therefore available to the Guest OS. This avoids the issue of memory being wasted for HT cores.
7. The CPU scheduler in vSphere 5.0 or later is very efficient and can intelligently schedule workload on a hyper-thread or a physical core depending on the VMs CPU demand. While the Exchange server will at some point be scheduled onto a HT thread, this is not likely to be for any extended duration or have any significant impact on performance.
8. Splitting the cluster into BCA’s and server workloads would increase the HA overhead, and effective reduce the usable compute capacity of the infrastructure.
9. Having a cluster with varying configurations (eg: HT enabled on some hosts and not others) is not advisable as it may lead to inconsistent performance and adds unnecessary complexity to the environment

Implications

1. In the event the vCPU to pCore ratio is > 2:1 for any reason (including HA event & Virtual Server Sprawl) the number of users supported and/or the performance of the Exchange environment may be impacted
2. DRS “Should” rules will need to be created to keep Exchange workloads on hosts with <2:1 vCPU to pCore ratio

 

 

 

VMware Host Isolation Response in a Nutanix Environment #NoSAN

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I was recently discussing the Nutanix solution with a friend of mine and fellow VCDX, Michael Webster (@vcdxnz001) and he asked what the recommended Host Isolation Response is for Nutanix.

At this stage I must advise there is no formal recommendation, but an Official vSphere on Nutanix Best Practice guide is in the works and will be released asap.

Back to my conversation with Michael, Being that Nutanix is an IP Storage solution, my initial feeling is that Host isolation Response should be set to “Shutdown”, but I didn’t go into any more detail with Michael, so I thought it best to post a quick explanation.

This post also assumes basic knowledge of vSphere as well as the Nutanix platform, for those of you who are not familiar with Nutanix please review the following links prior to reading the remainder of this post.

About Nutanix | How Nutanix Works | 8 Strategies for a Modern Datacenter

So back on topic, in other posts I have written for IP Storage, such as (Example Architectural Decision – Host Isolation Response for IP Storage) I have concluded that “Shutdown” was the most suitable setting and recommended specifying isolation addresses of the NAS controllers.

But as Nutanix changes the game and has one virtual storage controller per ESXi host, so does this change the recommendation?

In short, No, but for those who are interested, here is why.

If we leave the default isolation address, (being the default gateway for ESXi Management), in the event the gateway is down, it will trigger an isolation response even if the rest of the network is operating fine, thus an unnecessary outage would occur.

If we configure das.isolationaddress1 & 2 with the Management IP address of any two Nutanix Controller VMs (192.168.1.x , 192.168.1.y in my below diagram) then an isolation response will only be triggered if both Nutanix Controller VMs (CVMs) are not responding, in which case, the VMs should be Shutdown as the Nutanix cluster may not be function properly with two Controllers offline concurrently as its configured by default for N+1 (or replication factor of “2” in Nutanix speak).

The below is a high level example of the above configuration.

NutanixHostIsolation

Related Articles

1. Example Architectural Decision – Host Isolation Response for a Nutanix Environment

2. Storage DRS and Nutanix – To use, or not to use, that is the question?

3. VMware HA and IP Storage

Storage DRS and Nutanix – To use, or not to use, that is the question?

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Storage DRS (SDRS) is an excellent feature which was released with vSphere 5.0 in late 2011. For those of you who are not familiar with SDRS I recommend reading the following article prior to reading the rest of this post as SDRS knowledge is assumed from now on.

Understanding VMware vSphere 5.1 Storage DRS

This post also assumes basic knowledge of the Nutanix platform, for those of you who are not familiar with Nutanix please review the following links prior to reading the remainder of this post.

About Nutanix | How Nutanix Works | 8 Strategies for a Modern Datacenter

Storage DRS & Nutanix – To use, or not to use, that is the question?

With Storage DRS (SDRS), both capacity and performance can be managed, but what should SDRS manage in a Nutanix environment?

Lets start with performance. SDRS can help ensure optimal performance of virtual machines by enabling the I/O metric for SDRS recommendations as shown in the screen shot below.

SDRSsettingsIOmetricCircledSmall

Once this is done, SDRS will evaluate I/O every 8 hours (by default) and where the configured latency threshold is exceeded, perform a cost/benefit analysis before deciding to make a migration recommendation or do nothing.

So the question is, does SDRS add value in a Nutanix environment from a performance perspective?

The Nutanix solution adopts the “Scale-out” methodology by having one (1) Nutanix Controller VM (CVM) per Nutanix Node (ESXi Host) and then presents NFS datastore/s to the vSphere cluster which are serviced by all CVMs. The CVMs use intelligent auto-tiering to ensure optimal performance. The way this works at a high level, is as follows.

Data is written to an SSD tier (either PCIe SSD such as Fusion-io or SATA SSD) before being migrated off to a SATA tier once the blocks are determined to be “Cold” and if/when required, promoted back the an SSD tier when they become “Hot” again for improved read performance.

As with other vendor storage solutions with auto tiering technologies (such as FAST-VP , FlashPools etc) the same recommendation around SDRS and the I/O metric is true for Nutanix, leave it disabled.

So, at this point we have concluded the I/O metric will be “Disabled”, lets move onto Capacity management.

The Nutanix solution presents large NFS datastore/s to the ESXi hosts (Nutanix nodes) which are shared across all ESXi hosts in one or more vSphere clusters.

When using SDRS, it can manage initial placement of a new Virtual machine based on the configured “Utilized Space” metric (shown below) to ensure there is not a capacity imbalance between the datastores in a datastore cluster, as well as move virtual machines around when new machines are provisioned to ensure the balance is maintained.

UtilizedSpaceSDRS

So this is a really good feature which I have and do recommend in several scenarios, however the Nutanix solution presents typical a small number of large NFS datastores to the vSphere cluster (or clusters) which are serviced by all Controller VMs (CVMs) in the Nutanix cluster. Using SDRS for initial placement does not add much (if any) value as the initial placement will almost always be on the same large NFS datastore.

Where actual physical capacity becomes an issue, space saving technologies such as compression can be enabled, or the environment can be granularly scaled by adding just a single additional Nutanix node which linearly scales the solution from both a capacity and performance perspective.

The only real choice is when you choose to present two (or more) datastores where one datastore leverage’s the Nutanix compression technology. This is a very easy scenario for a vSphere admin to choose the placement of a VM and is the same amount of administrative effort as choosing a datastore cluster which would be a collection of datastores either using compression, or not depending on the workloads.

As a result there is no advantage to using SDRS to manage utilized space.

In conclusion, Storage DRS is a great feature when used with storage arrays where performance does not scale linearly or provide intelligent tiering to address I/O bottlenecks and/or where your environment has large numbers of datastores where you need to actively manage capacity.

As performance and capacity management are intelligently managed natively by the Nutanix solution, the requirement (or benefit) provided by SDRS is negated, as a result there is no requirement or benefit for using SDRS with a Nutanix solution.

Related Articles

1. Example Architectural Decision – VMware DRS automation level for a Nutanix environment