Tag Archives: hyper-v

What if my VMs storage exceeds the capacity of a Nutanix node?

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I get this question a lot, What if my VM exceeds the capacity of the node its running on. The answer is simple, the storage available to a VM is the entire storage pool which is made up of all nodes within the cluster and is not limited to the capacity of any single node.

Let’s take an extreme example, a single VM is running on Node B (shown below) and all other nodes have no workloads. Regardless of if the nodes are “Storage only” such as NX-6035C or any Nutanix node capable of running VMs e.g.: NX3060-G4 the SSD and SATA tiers are shared.

AllSSDhybrid

The VM will write data to the SSD tier and only once the entire SSD tier (i.e.: All SSD in all nodes) reaches 75% capacity will ILM tier the coldest data off the to SATA tier. So if the SSD tier never reaches 75% you will have all data in SSD tier both local and remote.

This means multiple CVMs (Nutanix Controller VM) will service the I/O which allows for single VMs to achieve scale up type performance where required.

As the SSD tier exceeds 75% data is tiered down to SATA but active data will still reside in SSD tier across the cluster and be serviced with all flash performance.

The below shows there is a lot of data in the SATA tier but ILM is intelligent enough to ensure hot data remains in the SSD tier.

AllSSDwithColdData

Now what about Data Locality, Data Locality is maintained where possible to ensure the overheads of going across the network are minimized but simply put, if the active working set exceeds the local SSD tier Nutanix ensures maximum performance by distributing data across the shared SSD tier (not just two nodes for example) and services I/O through multiple controllers.

In the worst case where the active working set exceeds the local SSD capacity but fits within the shared SSD tier, you will have the same performance as a Centralised All Flash Array, in the best case, Data Locality will avoid the requirement to traverse the IP network and service reads locally.

If the active working set exceeds the shared SSD tier, Nutanix also distributes data across the shared SATA tier and services I/O from all nodes within the cluster as explained in a recent post “NOS 4.5 Delivers Increased Read Performance from SATA“.

Ideally I recommend sizing the Active working set of VMs to fit within the local SSD tier but this is not always possible. If you’re running Nutanix you can find out what the active working set of a VM is via PRISM (See post here) and if you’re looking to size for a Nutanix solution, use my rule of thumb for sizing for storage performance in the new world.

How to view a VMs Active Working Set in PRISM

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Knowing a Virtual Machines Active Working Set is critical to ensuring all flash performance in any hybrid storage solution (Flash + SAS or SATA).

Because this is so critical, Nutanix has tracked this information for a long time via the hidden 2009 page. However as this information being available has proven to be so popular, it was included in PRISM in the latest release of Nutanix Acropolis Base Version 4.5.

The working set size for a virtual machines active working set can be viewed on a per vdisk basis across all supported hypervisors including ESXi, Hyper-V, KVM and the Acropolis Hypervisor (AHV).

To view this information, from the “Home” screen of PRISM, select the “VM” as shown below:

Note: The following screen shots were taken from an environment running Acropolis Base Version 4.5 and Acropolis Hypervisor 20150921 but the same process is applicable to any hypervisor.

PRISMVMmenu

Next highlight the Virtual Machine you wish to view details on, In the example below VM “Jetstress01” has been highlighted.VMlist

Below the above section you will see the VM summary as shown below. To view the working set size, Select “Virtual Disks” then the “Additional Stats” option which will show the following display:WorkingSetSizeAdditionalDetailsAs we can see the following information is displayed on a per vdisk granularity:

  1. Read / Write Latency
  2. Total IOPS
  3. Random IO percentage
  4. Read Throughput from Extent Cache / SSD and HDD
  5. Read Working set size
  6. Write Working set size
  7. Union Working set size

With the above information it is easy to calculate what node type and SSD capacity is most suitable for the virtual machine. This is something I would recommend customers running business critical applications check out.

If the “Read Source HDD” is showing frequent throughput and performance is lower than desired, moving the VM to a node with a larger SSD capacity will help performance. Alternatively if there are no nodes with a larger SSD tier, enabling in-line compression and/or Erasure Coding can help increase the effective SSD tier capacity and allow a larger working set size to be served from SSD.

If compression and EC-X are enabled and the SSD tier is still insufficient, additional nodes with larger SSD tier can be non disruptively added to the cluster and the virtual machine/s migrated regardless of hypervisor.

Acropolis Base Version 4.5 adds a lot of enhancements such as this so I recommend customers perform the one click upgrade and start exploring and utilizing this additional information.

MS Exchange on Nutanix Acropolis Hypervisor (AHV)

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While Virtualization of MS Exchange is now common across multiple hypervisors it continues to be a hotly debated topic. The most common objections being cost (CAPEX), the next being complexity (which translates to CAPEX & OPEX) and the third being that virtualization adds minimal value as MS Exchange provides application level high availability. The other objection I hear is Virtualization isn’t supported, which always makes me laugh.

In my experience, the above objections are typically given in the context of a dedicated MS Exchange environment, which in that specific context some of the points have some truth, but the question becomes, how many customers run only MS Exchange? In my experience, None.

Customers I see typically run tens, hundreds even thousands of workloads in their datacenters so architecting silos for each application is what actually leads to cost & complexity when we think outside the box.

Since most customers have virtualization and want to remove silos in favour of a standarized platform, MS Exchange is just another Business Critical Application which needs to be considered.

Let’s discuss each of the common objections and how I believe Acropolis + Nutanix XCP addresses these challenges:

Microsoft Support for Virtualization

For some reason, there is a huge amount of FUD regarding Microsoft support for Virtualization (other than Hyper-V), but Nutanix + Acropolis is certified under the Microsoft Server Virtualization Validation Program (SVVP) and runs on block storage via iSCSI protocol, so Nutanix + Acropolis is 100% supported for MS Exchange as well as other workloads like Sharepoint & SQL.

Cost (CAPEX)

Unlike other hypervisors and management solutions, Acropolis and Acropolis Hypervisor (AHV) come free with every Nutanix node which eliminates the licensing cost for the virtualization layer.

Acropolis management components also do not require purchase or installation of Tier 1 database platforms, all required management components are built into the distributed platform and scaled automatically as clusters are expanded. As a result, even licenses for Windows operating system are not required.

As a result, Nutanix + Acropolis gives Exchange deployments all the Virtualization features (below) which provide benefits at no cost.

  • High Availability & Live Migration
  • Hardware abstraction
  • Performance monitoring
  • Centralized management

Complexity (CAPEX & OPEX)

Nutanix XCP + Acropolis can be deployed in a fully optimal configuration from out of the box to operational in less than 60 minutes. This includes all required management components which are automatically deployed as part of the Nutanix Controller VM (CVM). For single cluster environments, no design/installation is required for any management components, and for multiple-cluster environments, only a single virtual appliance (PRISM Central) is required for single pane of glass management across all clusters.

Acropolis gives Exchange deployments all the advantages of Virtualization without:

  • Complexity of deploying/maintaining of database server/s to support management components
  • Deployment of dedicated management clusters to house management workloads
  • Having onsite Subject Matter Experts (SMEs) in Virtualization platform/s

Virtualization adds minimal value

While applications such as Exchange have application level high availability, Virtualization can further improve resiliency and flexibility for the application while making better use of infrastructure investments.

The Nutanix XCP including Acropolis + Acropolis Hypervisor (AHV) ensures infrastructure is completely abstracted from the Operating System and Application allowing it to deliver a more highly available and resilient platform.

Microsoft advice is to limit the maximum compute resources per Exchange server to 24 CPU cores and 96GB RAM. However with CPU core counts continuing to increase, this may result in larger numbers of servers being purchased and maintained where an application specific silo is deployed. This would lead to increased datacenter and licensing costs not to mention operational overhead of managing more infrastructure. As a result, being able to run Exchange alongside other workloads in a mixed environment (where contention can easily be avoided) reduces the total cost of infrastructure while providing higher levels of availability to all workloads.

Virtualization allows Exchange servers to be sized for the current workload and resized quickly and easily if/when required which ensures oversizing is avoided.

Some of the benefits include:

  • Minimizing infrastructure in the datacenter
  • Increasing utilization and therefore value for money of infrastructure
  • Removal of application specific silos
  • Ability to upgrade/replace/performance maintenance on hardware with zero impact to application/s
  • Faster deployment of new Exchange servers
  • Increase availability and provide higher fault tolerance
  • Self-healing capabilities at the infrastructure layer to compliment application level high availability
  • Ability to increase Compute/Storage resources beyond that of the current underlying physical server (Nutanix node) e.g.: Add storage capacity/performance

The Nutanix XCP Advantages (for Exchange)

  • More usable capacity

With features such as In-Line compression giving between 1.3:1 and 1.7:1 capacity savings & Erasure Coding providing up to a further 60% usable capacity, Nutanix XCP can provide more usable capacity than RAW while providing protection from SSD/HDD and entire server failures.

In-Line compression also improved performance of the SATA drives, so its a Win/Win. Erasure coding (EC-X) stores data in a more efficient manner which allows more data to be served from the SSD tier, also a Win/Win.

  • More Messages/Day and/or Users per physical CPU core

With all Write I/O serviced by SSD the CPU WAIT time is significantly reduced which frees up the physical CPU to perform other activities rather than waiting for a slow SATA drive to respond. As MS Exchange is CPU intensive (especially from 2013 onwards) this means more Messages per Day and/or Users can be supported per MSR VM compared to physical servers.

  • Better user experience

As Nutanix XCP is a hybrid platform (SSD+SATA), newer/hotter data is serviced by the SSD tier which means faster response times for users AND less CPU WAIT which also helps further increase CPU efficiencies, again leading to more Messages/Day and/or Users per CPU core.

Summary:

With Cost (CAPEX), Complexity (CAPEX & OPEX) and supportability issues well and truly addressed and numerous clear value adds, running a business critical application like MS Exchange on Nutanix + Acropolis Hypervisor (AHV) will make a lot of sense for many customers.