Introduction to Nutanix cluster components

In this article I will briefly explain about the different components of a Nutanix cluster. The major components are listed below.

Nutanix cluster components

1. Stargate: Data I/O manager for the cluster.
2. Medusa: Access interface for Cassandra.
3. Cassandra: Distributed metadata store.
4. Curator: Handles Map Reduce cluster management and cleanup.
5. Zookeeper: Manages cluster configuration.
6. Zeus: Access interface for Zookeeper.
7. Prism: Management interface for Nutanix UI, nCLI and APIs.

Stargate

• Responsible for all data management and I/O operations.
• It is the main point of contact for a Nutanix cluster.
• Workflow: Read/ write from VM < > Hypervisor < > Stargate.
• Stargate works closely with Curator to ensure data is protected and optimized.
• It also depends on Medusa to gather metadata and Zeus to gather cluster configuration data.

Medusa

• Medusa is the Nutanix abstraction layer that sits infront of DB that holds the cluster metadata.
• Stargate and Curator communicates to Cassandra through Medusa.

Cassandra

• It is a distributed high performance and scalable DB.
• It stores all metadata about all VMs stored in a Nutanix datastore.
• It needs verification of atleast one other Cassandra node to commit its operations.
• Cassandra depends on Zeus for cluster configuration.

Curator

• Curator constantly access the environment and is responsible for managing and distributing data throughout the cluster.
• It does disk balancing and information life cycle management.
• It is elected by a Curator master node who manages the task and job delegation.
• Master node coordinates periodic scans of the metadata DB and identifies cleanup and optimization tasks tat Stargate or other components should perform.
• It is also responsible for analyzing the metadata, this is shared across all Curator nodes using a Map Reduce algorithm. 

Zookeeper

• It runs on 3 nodes in the cluster.
• It can be increased to 5 nodes of the cluster.
• Zookeeper coordinates and distributes services.
• One is elected as leader.
• All Zookeeper nodes can process reads.
• Leader is responsible for cluster configuration write requests and forwards to its peers.
• If leader fails to respond, a new leader is elected.

Zeus

• Zeus is the Nutanix library interface which all other components use to access cluster configuration information.
• It is responsible for cluster configuration and leadership logs.
• If Zeus goes down, all goes down!

Prism

• Prism is the central entity of viewing  activity inside the cluster.
• It is the management gateway for administrators to configure and monitor a Nutanix cluster.
• It also elects a node.
• Prism depends on data stored in Zookeeper and Cassandra.

Note: All the info provided above are based on Nutanix 4.5 Platform Professional (NPP) administration course.

Creating HTML report of ScaleIO cluster using PowerShell

This post is a reference to a small reporting script for ScaleIO environments. The project will generate a brief HTML report of your ScaleIO Ready Node SDS infrastructure (with AMS - Automated Management Services) by making use of ScaleIO Ready Node AMS REST APIs and PowerShell. The report provides information about MDM cluster state, overall cluster capacity, system objects, alerts, and health state of all disks in the cluster. Here the API is available as part of ScaleIO Ready Node AMS. These AMS REST API allows you to query information and perform actions related to ScaleIO software and ScaleIO Ready Node hardware components. To access the API you need to provide AMS username and password. Responses returned by AMS server are formatted in JSON format.

Project reference: https://github.com/vineethac/sio_report

Use case: This script can be used/ leveraged as part of daily cluster health/ stats reporting process, or something similar; so that monitoring Engineers or whoever responsible can have a look at it on a daily basis to make sure everything is healthy and working normal. 

Related references:

Working with ScaleIO REST API using PowerShell - Part 1

Working with ScaleIO REST API using PowerShell - Part 2

Working with ScaleIO REST API using PowerShell - Part 3

Hope this was helpful. Cheers!

Software Defined Storage using ScaleIO

In this article I will explain briefly about ScaleIO and various options that are available to deploy ScaleIO software defined storage (SDS) solution. 

ScaleIO can be considered as a very good option for customers who are moving towards deploying software defined storage  solutions and hyperconverged infrastructure. As ScaleIO software supports multiple hypervisors and operating systems like VMware ESXi, Hyper-V, RHEL, Windows etc. customers with a heterogeneous IT infrastructure gets the most benefit out of it. Apart from that it offers multiple deployment modes like hyperconverged, two layer and mixed mode. I am sure most of you are very much familiar with the term hyperconverged where compute and storage runs together on the same box. You can scale both compute and storage resources together by adding more and more nodes to your cluster. A two layer mode is nothing but a storage only configuration where you can scale the storage resources separately. It is essentially a virtual SAN infrastructure implemented using ScaleIO SDS. A mixed mode scenario will usually occur when transitioning from storage only configuration to hyperconverged.

Now I will just give an overview on how to deploy ScaleIO on VMware and RHEL platforms. ScaleIO has tight integration with VMware and they provide a powershell script and vCenter plugin to simplify the deployment. In case of RHEL platform, you can use Installation Manager (IM) which is a part of ScaleIO Gateway for quick and easy deployment of ScaleIO cluster. Customers have multiple options to consume ScaleIO. They can just buy the ScaleIO software alone and use commodity x86 hardware to build the cluster (not a great idea for production deployments as they have to figure out and use the validated/ qualified hardware and software components to ensure seamless operation and proper support) or they can buy ScaleIO Ready Nodes which are prevalidated, preconfigured and optimized PowerEdge servers to deploy ScaleIO cluster. Apart from that there is another offering VxRack System Flex which is a rack-scale hyperconverged solution built on Dell EMC PowerEdge servers with integrated Cisco networking and ScaleIO software. 

Lets have a look at the major components of ScaleIO. Below figure shows a 5 node hyperconverged ScaleIO cluster running on a highly available VMware platform. The three main components of ScaleIO are:

• SDC - ScaleIO Data Client
• SDS - ScaleIO Data Server
• MDM - Meta Data Manager

In this scenario, all 5 nodes have ESXi installed and clustered. All nodes have local hard disks present in them. And its the responsibility of ScaleIO software to pool all the hard disks from all 5 nodes forming a distributed virtual SAN.

SDC is a light weight driver which is responsible for presenting LUNs provisioned from the ScaleIO system. SDS is responsible for managing local disks present in each node. MDM contains all the metadata required for system operation and configuration changes. It manages the metadata, SDC, SDS, system capacity, device mappings, volumes, data protection, errors/ failures, rebuild and rebalance operations etc. ScaleIO supports 3 node/ 5 node MDM cluster. Above figure shows a 5 node MDM cluster, where there will be 3 manager MDMs and out of which one will be master and two will be slaves and there will be two Tie-Breaker (TB) which helps in deciding master MDM by maintaining a majority in the cluster. In a production environment with 5 or more nodes, it is recommended to use a 5 node MDM cluster as it can tolerate 2 MDM failures.

ScaleIO uses a distributed two way mesh mirror scheme to protect data against disk or node failures. To ensure QoS it has the capability where you can limit bandwidth as well as IOPS for each volume provisioned from a ScaleIO cluster. And regarding scalability a single ScaleIO cluster supports upto 1024 nodes. In very large ScaleIO deployments it is highly recommended to configure separate protection domains and fault sets to minimize the impact of multiple failures at the same time. 

You can download ScaleIO software for free to test and play around in your lab environment.

References:
Dell EMC ScaleIO Basic Architecture
Dell EMC ScaleIO Design Considerations And Best Practices
Dell EMC ScaleIO Ready Node

Storage Spaces Direct - Volumes and Resiliency

Storage Spaces Direct (S2D) is the Microsoft implementation of software defined storage (SDS). This article briefly explains about the different types of volumes that can be created on a S2D cluster. Once you enable S2D using Enable-ClusterS2D cmdlet, it will automatically claim all physical disks in the cluster and forms a storage pool. On top of this pool you can create multiple volumes which is explained below.

Mirror

• Recommended for workloads that have strict latency requirements or that need lots of mixed random IOPS
• Eg: SQL Server databases or performance-sensitive Hyper-V VMs
• If you have a 2 node cluster: Storage Spaces Direct will automatically use two-way mirroring for resiliency
• If your cluster has 3 nodes: it will automatically use three-way mirroring
• Three-way mirror can sustain two fault domain failures at same time

new-volume -friendlyname "Volume A" -filesystem CSVFS_ReFS -storagepoolfriendlyname S* -size 1TB

• You can create two-way mirror by mentioning "PhysicalDiskRedundancy 1"

new-volume -friendlyname "Volume A" -filesystem CSVFS_ReFS -storagepoolfriendlyname S* -size 1TB -PhysicalDiskRedundancy 1

Parity

• Recommended for workloads that write less frequently, such as data warehouses or "cold" storage, traditional file servers, VDI etc.
• For creating dual parity volumes min 4 nodes are required and can sustain two fault domain failures at same time

new-volume -friendlyname "Volume B" -filesystem CSVFS_ReFS -storagepoolfriendlyname S* -size 1TB -resiliencysettingname Parity

• You can create single parity volumes using the below

new-volume -friendlyname "Volume B" -filesystem CSVFS_ReFS -storagepoolfriendlyname S* -size 1TB -resiliencysettingname Parity -PhysicalDiskRedundancy 1

Mixed/ Tiered / Multi-Resilient (MRV)

• In Windows Server 2012 R2 Storage Spaces, when you create storage tiers you dedicated physical media devices. That means SSD for performance tier and HDD for capacity tier
• But in Windows Server 2016, tiers are differentiated not only by media types; it can include resiliency types too
• MRV = Three-way mirror + dual-parity
• In a MRV, three-way mirror portion is considered as performance tier and dual parity portion as capacity tier
• Recommended for workloads that write in large, sequential, such as archival or backup targets
• Writes land to mirror section of the volume and then it is gradually moved/ rotated in to parity portion later
• Each MRV by default will have 32 MB Write-back cache 
• ReFS starts rotating data into the parity portion at 60% utilization of the mirror portion and gradually as utilization increases the speed of data movement to parity portion also increases
• You should have min 4 nodes to create a MRV

new-volume -friendlyname "Volume C" -filesystem CSVFS_ReFS -storagepoolfriendlyname S* -storagetierfriendlynames Performance, Capacity -storagetiersizes 1TB, 9TB

References:

Microsoft

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