Category Archives: Storage

Understanding vSphere Storage Latency – Part I

Troubleshooting any performance related issue could be quite daunting. In any virtualized platform there are additional layers of indirection, hence we need to invoke a layered approach to troubleshoot and resolve such issues.

In this blog series, we shall breakdown the various components and how we can identify if a specific component is contributing to the storage latency.

Types of Storage

Storage can be broadly classified into three types,

  • File-Based Storage
  • Block storage
  • Object Storage

Here is a nice blog outlining a definition and usecases for each of them  Storage types

In the context of vSphere,

  • A File-based storage is provisioned through NFS
  • A block based storage is provisioned via iSCSI & Fiber Channel
  • VVOLs and vSAN represent object based storage (although with subtle variations)

Now lets take a closer look at storage architecture and its components specifically around block storage.

Storage Architecture & Components

In the following diagram, we have broken down the components into 7 layers that can be isolated from a troubleshooting standpoint,Screen Shot 2018-01-03 at 9.41.32 PM

  1. In a typical block storage architecture, the most fundamental component is the hard disk. Hard disks have evolved over a period of time from magnetic disks to flash/solid state drives to NVMe. This forms our first layer.
  2. LUN/RAID groups – The hard disks are seldom presented in raw form to the servers in a datacenter setup, A set of hard disks are grouped together as logical units for optimizing performance, availability and security. These are typical referenced as LUNs(Logical Unit Number) in a SAN environment.
  3. The points of entry into a storage array are termed differently by different vendors as Controllers, Storage Processors, Directors or simply array front end ports. Server can connect directly to the controllers or through fabric switches.
  4. SAN/Fabric or Network Switch aids in multipathing and eliminating single points of failure my being an intermediary between the servers and storage array. In an FC SAN, these are termed as fabric switches , in the context of iSCSI or NFS, the existing network switches play the same role
  5. The physical connectivity is enabled through fiber channel cabling or ethernet cables for FC & iSCSI/NFS respectively
  6. Host Bus Adapter or Network Interface Cards are exit or entry points for I/O,  subsequently the drivers enable the devices
  7. Hypervisor Layer introduces specific path/component within the kernel depending on the type of virtual disks associated to a VM, for instance an Virtual RDM follows a different I/O path from a standard vmdk within the kernel

Now that we have outlined the different components in the architecture, next we shall understand how to isolate a performance bottleneck at the different layers.

Getting Started with VMware Virtual VSAN

“Why do we have to listen to our hearts?” the boy asked, “Because, wherever your heart is, that is where you’ll find your treasure.”

– “The Alchemist” by Paulo Coelho

In pursuit of my dreams, I debut as an author.

A blurb about the book,

Title :  “Getting started with VSAN”

Build an optimal, high performance and resilient software defined storage on VSAN for your vSphere infrastructure


  • Effectively understand the fundamental concepts and features of Virtual SAN
  • Implement and administer your VMware VSAN efficiently
  • Ensure stability, data reliability and meet service level agreements for each virtual machine and application

Virtual SAN without any doubt is the latest fad in the Virtualization Arena. The concept has taken Datacenter Virtualization to the next level by moving the storage back from SAN to server hardware. The best part of VSAN solution is the fact that a near flash performance is achieved with only a marginal percentage of flash storage. And all this with hardly any compromise to the exquisite feature set of vSphere and interoperability with other product suite from VMware. This book helps in closely examining the capabilities as well the limits of VSAN in a sequential flow while explaining the fundamental aspects.

This book covers the fundamental aspects of Software Defined storage, its evolution and its role in a Software-Defined Data Center. You will have a complete understanding of VMware Virtual SAN architecture, its components and how it is put together. Guidelines pertaining to sizing and profiling of Virtual Machines are also covered in detail.

The book explores your options in choosing the type of Virtual SAN and deploys a simple setup that would demonstrate to you the workflow of a VSAN deployment. You will review policy based management of storage and see how Storage Policy-Based Management modernizes storage provisioning and paves the way for being truly software defined.

After covering the anatomy of I/O-Input/Output to a VSAN datastore, some insight into design considerations and best practices of VSAN configuration, the book ends with a discussion on troubleshooting and how various utilities can be leveraged to diagnose common problems that surface on a Virtual SAN environment.

What you will learn

  • Understand what Software Defined Storage is and how it is implemented through VMware Virtual SAN
  • Install, Configure and Administer VSAN
  • Architect VSAN to cater to the specific business requirements
  • Define Storage Tiering at the software layer by implementing Storage Policy-Based Management
  • Understand how every I/O flows through the VSAN infrastructure
  • Monitor your VSAN Infrastructure to discover issues at an early stage
  • Efficiently use utilities to troubleshoot and fix issues

Who this book is written for

This book is intended for Server Administrators and Storage Administrators who would like to successfully build and scale a VSAN backed vSphere infrastructure. Basic understanding of vSphere concepts and storage fundamentals will be helpful.

Style and approach

A simple step-by-step guide to walk you in-depth through software defined storage and virtual VSAN. Each chapter is written keeping in mind that the audience are not particularly storage experts rather server administrators.

Where can you get it

The book is available @

Do feel free to write to me with your feedback at

Cheers !!!

Metadata & Data Integrity issues observed in certain conditions with VMFS volumes

Objective of this article is to understand the types, causes and remediation of data integrity issues that may manifest in a VMFS volume.

Types of Corruption

The data integrity issues may arise on two different segments in a volume

  1. Metadata
  2. Data

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