How Virtual Machine data is stored and managed within a HPE SimpliVity Cluster – Part 2

In my previous blog post my aim was to paint a picture of how data, that makes up the contents of a virtual machine is stored within a HPE SimpliVity Cluster. I introduced the concept of both primary and secondary data containers, their creation process, placement, and how we report on physical cluster capacity.

If you are unfamiliar with any of thees concepts, I suggest reading that post here before continuing 🙂

Now that we have a greater understanding of how virtual machine data is stored we can start to dig a little deeper to understand how the DVP automatically manages this data, and as administrators, how we can manage this data as the environment grows.

There is a lot to cover in this topic and in the interest of trying keeping this post concise and building on core concepts incrementally I will concentrate automatic management of data via IWO. I will focus on other automatic data management features (via Auto Balancer) and manual management of data in future posts.

This post has been co-authored with my colleague Scott Harrison, a big thank you to Scott as he has provided and posed some interesting points to consider.


Automatic Management of Data

IWO, a closer look

As previously stated, a core feature of the HPE SimpliVity DVP is IWO (Intelligent Workload Optimizer).

IWO is comprised of two sub components, The Resource Balancing Service and the VMware DRS / SCVMM PRO Integration Service. For the this post I will focus on the VMware DRS integration service, however the architecture remains analogous for Hyper-V.

IWO’s aim is two fold…

1. Ensure all resources of a cluster are properly utilized.

This process is handled by the Resource Balancing Service both at initial virtual machine creation and proactively throughout the life cycle of the VM and its associated backups. This is all achieved without end-user intervention.

2. Enforce data locality.

This process is handled by the VMware DRS / SCVMM PRO integration service by pinning (through VMware DRS affinity rules or Hyper-V SCVMM PRO) a virtual machine to nodes that contain a copy of that data. Again this is all achieved without end-user intervention.

Note ! The resource balancing service is an always on service and does not rely on VMware DRS to be active and enabled on a VMware cluster, it works independently from the DRS integration service.


Ensuring all resources of a cluster are properly utilized 

VM & Data Placement Scenarios

The primary goal of IWO via the resource balancer service is to ensure that no single node within a cluster experiences undue utilization of any one particular resource: CPU, memory, storage capacity, and I/Os. The objective is not that each node experiences the same utilization across all resources or dimensions (that may be impossible) but instead, ensures that each node has sufficient headroom in terms of physical storage capacity to handle expected future demand and that no single node is handling a much larger number of I/Os relative to its cluster peers.

The resource balancing service will use different optimization criteria for different scenarios. For example, initial VM placement on a new cluster (i.e. migration of existing VMs from a legacy system), best placement of a newly created VM within an existing system, Rapid Clone of an existing VM and VDI-specific optimizations for handling linked clones.

Lets explore the different scenarios…

Scenario #1 New VM Creation – VMware DRS enabled and set to Fully Automated

When creating or storage v-motioning a virtual machine to a HPE SimpliVity Host / Datastore vSphere DRS will automatically place the VM on a node with relatively low CPU & memory utilization according to its own algorithms (default DRS algorithms). No manual selection of a Node is necessary.

DRS Set to Fully Automatic – The VMware Cluster is selected as the compute resource – DRS automatically selects an ESXi server to run the VM


In the below diagram VMware DRS has chosen Nodes 3 and 4 respectively to house VM’s 1 and 2. Independently, the DVP has chosen a pair of ”least” utilized nodes within the cluster (according to Storage Capacity and I/O Demand) for the data containers of those VM’s to be placed.

VM-1 and VM-2 have been placed on nodes 1 & 2 and 3 & 4 respectively via the resource balancer service.

IWO via the DRS integration service will pin VM-1 to Node 1 & 2 and VM-2 is to Nodes 3 & 4 by automatically creating and populating DRS rules into vCenter. Lets look at how that is achieved.

How are DRS Rules Created ?

Each DRS rule consists of the following components:

  • A Virtual Machine DRS Group.
  • A Host DRS Group.
  • A Virtual Machines to Hosts rule. This consists of “must run on these hosts”, “should run on these hosts”, “must not run on these hosts”, or “should not run on these hosts”. For HPE SimpliVity we use the “should run on these hosts” rule.


In our example it is not optimal for VM-1 to be running on node 4 as all of the I/O for the VM must be forwarded to either Node 1 or Node 2 in order to be processed.  If the VM can be moved automatically to those nodes, then one hop is eliminated from the I/O path.

First a Virtual Machine DRS Group is created, as we’re looking to make a group of virtual machines that will run optimally on two nodes. In our case the name of the Virtual Machine DRS Group will be SVTV_<hostID2>_<hostID3> as we’re looking to make a group of virtual machines that will run on these two nodes.

Below we can see VM-1 assigned to this VM Group. VM-1 will share this group with other Virtual Machines that have their data located on the same nodes. Note the Host ID is a GUID and not an IP address or Hostname etc of the node, while this may appear confusing to the end user this is the actual GUID of the HPE SimpliVity node. Unfortunately mapping the GUID to the hostname or IP address of the node is not possible through the GUI and will require the command “dsv-balance-show –showNodeIP” if you do wish to identify the Node IP.

drs vm group
DRS VM Group containing VM-1


balance show
dsv-balance-show –ShowNodeIP – we can map the output of this command (node GUID) to the VM Group

Looking at the VM Group for VM-1 we can deduce that the data is stored on nodes ending in “aaf and 329” which in-turn equates to OVC .185 and .186 which in turn live on esxi Nodes ending in 81 and 82 as shown below.

Again all of this is handled automatically for you, however for the post to make sense it is important to know where these values come from.

Identifying the Node(Host) associated with the OVC VM

Secondly, Host DRS Groups are created,  they are named SVTH_<hostID2>_<hostID3>. The Host groups will only ever contain two nodes as the virtual machines only contain data on two nodes. There will be several host groups created depending on how many Hosts there are in the cluster, one host group for each combination of nodes. Here I have highlighted the host group for hosts 81 and 82 which the VM-1 will be tied to.

drs host group

Last a “Virtual Machines to Hosts” rule is made that directs DRS that the VM-1 “should run on” the hosts 81 and 82 , i.e. a HPE SimpliVity rule consist of a HPE SimpliVity host group and a SimpliVity VM group.

DRS affinity rules are should rules and not must rules. This is an important distinction  that we will discuss later in the post.

DRS Rule “Run VMs On Hosts” containing appropriate Host Group and VM Group for VM-1

If set to Fully Automated VMware DRS will vMotion any VM’s violating these rules to one of the data container holding nodes, thus aligning the VM with its data. In our case VM-1 was violating the affinity rules by virtue of being placed on Node 4 and is automatically v-motioned to node 2 via DRS.


Scenario #2 New VM Creation  – VMware DRS Disabled

As stated previously, if VMware DRS is not enabled the Resource Balancer Service continues to function and initial placement decisions continue to operate, however DRS affinity rules will not be populated into to vCenter.

drs manual
DRS Disabled – User must select a compute resource within the cluster

In this scenario when Virtual Machines are provisioned they may reside on a node where there is no data locality. A HPE SimpliVity alarm “VM Data Access Not Optimized” will be generated at the VM object layer within vCenter alerting the user.

not optimized
Data Access Not Optimized refers to a virtual machine running on a host where there is no local copy of the VM Data

The HPE SimpliVity platform through interacting with vCenter Tasks and Events will generate an event and remediation steps directing you to which nodes contain a copy of the Virtual Machine data. In the below diagram I have highlighted the “Data access is not optimized” event that directs the user to v-motion the VM to the outlined hosts.

data access not optimized
Data Access not optimized alarm directing the user to v-motion the VM to one of the outlined hosts

Rapid clone of an existing VM

We have shown how the resource balancing service behaves in regard to new VM creation, however the resource balancing service takes a different approach for HPE SimpliVity Clones and VMware Clones of Virtual Machines (VMware clones can also be handled by HPE SimpliVity via the VAAI plugin for faster operation).

In this scenario the Resource Balancer service will leave cloned VM data on the same nodes as the parent as this achieves best possible cluster-wide storage utilization & de-duplication ratios.

Resource Balancer service will place clones on the same nodes as their parents

If I/O demand exceeds node capabilities the DVP will live-migrate data containers in the background to less-loaded node(s).

hive migration
Automatic Migration of Cloned Data Containers, followed by automatic v-motion of VM due to auto update of affinity rules after data container migration (nice!)

Live migration of a data container does not refer to VMware storage v-motion. It refers to the active migration of a VM Data Container to another Node.

VDI specific optimizations for handling linked clones

The scope of VDI and VDI best practices is beyond this post however I did want to mention how the HPE SimpliVity platform handles this scenario. VDI environments typically clone a VM, or golden image, many times. These clones essentially become read only templates for new desktops.

VDI Setup – Clone Templates from a Golden Image


As VDI desktops are deployed, linked clones are created on random hosts. Linked clones mostly read from the read only templates and write locally which causes proxying and adds extra load to the nodes that host the read only templates.

Deployed VDI VM’s – Mainly reads from cloned golden image causing I/O to be Proxied over network

To mitigate against this the Resource Balancer service will automatically distribute read-only master images across all nodes for even load. This aligns linked clones with their parents to ensure node-local access. It is also worth noting that Resource Balancer may also relocate links clones.

Linked clones automatically aligned with their parents to ensure node local Read/Writes


Thoughts on initial placement


Now that we have an understanding of initial placement lets explore some of the finer points and interactions between DRS and IWO.

That’s all well and good I hear you say,  but what if DRS has chosen a viable node based on available CPU and Memory (or whatever other DRS rules we have set it) and the DVP has placed the primary and secondary data containers on two other nodes which may be more CPU and Memory constrained ? or what if you as the administrator want more granular control ?

Firstly, storage is always the primary concern right ? DRS does not have access to underlying storage utilization figures nor is even designed with this in mind, its only concerns are CPU and Memory resources of the cluster as a whole, HPE SimpliVity through the DVP must take storage into account when placing data.

If this scenario is indeed encountered then DRS will be forced to re-calculate cluster resources and may move other VM’s (according to their affinity rules) to re-balance load after the new affinity rule(s) are populated and enacted upon for any new virtual machines added to the cluster. Again this process is dynamic both from a HPE SimpliVity and VMware DRS point of view.

It is also recommended to Separate workloads where possible, for example, server-based and VDI workloads into separate clusters.

The HPE SimpliVity DRS rules are “Should” rules and thus during a HA event, this rule will be overwritten in order to keep the VM’s running. DRS makes a best effort to optimize according to existing IWO rules, but in some high load environments DRS will ignore IWO. This can result in VM’s being run on a node other than their primary or secondary storage nodes.

Secondly, what if you as the administrator want more granular control ? In this scenario IWO and the Resource Balancer service can be disabled however, this is only recommended with the advice of support for specific circumstances and is beyond the scope of this post. Suffice to say Resource Balancer in conjunction with IWO designed to be zero touch.


Disabling the Resource Balancer 


Why? It is not recommend to disable Resource Balancer as its algorithms are designed for, and cater to all scenarios, however for specific use cases and architectures it may be beneficial to temporarily disable Resource Balancer, this will of course require a more hands on approach to overall data management.

Resource Balancer is enabled by default and uses the BALANCED placement algorithm  for initial VM placements (existing VM’s transferred into the system) and the BEST_FIT for provisioning new VM’s. As outlined in this post BEST_FIT  and BALANCED take into account Storage Capacity and I/O Demand of all nodes in the cluster when deciding where to place the primary and secondary data containers.

Issue the command “dsv-balance-show –status” to view the status of Resource Balancer

balance show
Output of dsv-balance-show –status command

Resource Balancer can be disabled on a per node basis if required. When Resource Balancer is disabled the VM provisioning algorithm will now be set to RANDOM and LOCAL_PRIMARY. This essentially means one of two things.

  1. If the user or DRS selects a particular node to house a VM from vCenter, this will happen. i.e. Resource Balance will not choose a better Node (as its offline).
  2. If virtual machines are being created at the cluster level within vCenter this node may randomly house a data container on a round robin provisioning .

Resource Balancer can be disabled on the node using the command “dsv-balance-disable”.

disbale resource balancer
disabling Resource Balancer


The Resource Balancer service can be re-enabled by the command “dsv-balance-enable”. Once re-enabled the Resource Balancer will service will default back to BEST_FIT and BALANCED within the overall cluster.


Checking the status of IWO


A cluster must contain three HPE OmniStack hosts to start creating cluster groups and affinity rules in DRS. A one or two-host cluster automatically accesses data efficiently and does not need affinity rules.

When you first deploy an HPE OmniStack host, the IWO setting defaults to enabled. If you deploy an HPE OmniStack host to a cluster that contains other HPE OmniStack hosts, IWO defaults to the setting used by the cluster. For example, if you changed the setting from enabled to disabled, the HPE OmniStack host joining the cluster takes on the disabled IWO setting.

You can also include standard ESXi hosts as long as they share an HPE SimpliVity datastore with another HPE OmniStack host in the cluster.

Use the command “svt-iwo-show” (from any node within the cluster)  to show if a cluster has Intelligent Workload Optimizer enabled or disabled. This will determine
whether the feature is active or not.

verifying the status of IWO


Disabling IWO


IWO can be disabled, unlike the Resource Balancer service, disabling IWO is a cluster wide operation not a node local operation. Disabling IWO will remove all HPE SimpliVity affinity rules from vCenter (or SCVMM).

To disable IWO issue the command “svt-iwo-disable”

Disabling IWO and verifying


iwo enabled
DRS Rules before IWO is disabled
iwo disabled
When IWO is disabled all HPE SimpliVity rules are removed automatically


Why? Again, it is not recommend to disable IWO, however for specific use cases and architectures it may be beneficial to temporarily disable IWO, this will of course require a more hands on approach to overall data management. A better alternative may be to set DRS to manual.


Enabling IWO


IWO can be re-enable using the command “svt-iwo-enable”. Once re-enabled DRS rules are automatically re-populated back into vCenter.

Enabling IWO
iwo enabled
DRS rules are automatically re-populated into vCenter

As a final note, do not enable vSphere Distributed Power Management (DPM) to ensure that it cannot shut down the HPE OmniStack Virtual Controller on a host after load balancing occurs


Management of Data as the environment grows 


The HPE SimpliVity platform will continue to manage cluster data as the environment grows and evolves. Auto Balancer works in conjunction with the IWO / Resource Balancer service and is focused on the management of VM Data containers within the cluster. Auto Balancer aim is to migrate data containers to other nodes within the cluster should it be required i.e. as data grows for a large VM’s a particular node may become overloaded. Auto Balancer will look for and migrate data containers to other less utilized nodes within the cluster.

We will discuss the Auto Balancer and manual management of Data in an upcoming post.