Book Image

Troubleshooting vSphere Storage

By : Mike Preston
Book Image

Troubleshooting vSphere Storage

By: Mike Preston

Overview of this book

Virtualization has created a new role within IT departments everywhere; the vSphere administrator. vSphere administrators have long been managing more than just the hypervisor, they have quickly had to adapt to become a ‘jack of all trades' in organizations. More and more tier 1 workloads are being virtualized, making the infrastructure underneath them all that more important. Due to this, along with the holistic nature of vSphere, administrators are forced to have the know-how on what to do when problems occur.This practical, easy-to-understand guide will give the vSphere administrator the knowledge and skill set they need in order to identify, troubleshoot, and solve issues that relate to storage visibility, storage performance, and storage capacity in a vSphere environment.This book will first give you the fundamental background knowledge of storage and virtualization. From there, you will explore the tools and techniques that you can use to troubleshoot common storage issues in today's data centers. You will learn the steps to take when storage seems slow, or there is limited availability of storage. The book will go over the most common storage transport such as Fibre Channel, iSCSI, and NFS, and explain what to do when you can't see your storage, where to look when your storage is experiencing performance issues, and how to react when you reach capacity. You will also learn about the tools that ESXi contains to help you with this, and how to identify key issues within the many vSphere logfiles.
Table of Contents (16 chapters)
Troubleshooting vSphere Storage
Credits
About the Author
Acknowledgment
About the Reviewers
www.PacktPub.com
Preface
Index

An I/O request – from start to finish


Now that we have a general understanding of how ESXi presents storage to a virtual machine and handles load balancing and failover, let's have a look at an I/O request from start to finish. The following figure shows a graphical representation of the following steps:

  • The VM issues a SCSI request to its respective virtual disk.

  • Drivers from within the guest OS communicate with the virtual storage adapters.

  • The virtual storage adapter forwards the command to the VMkernel where the PSA takes over.

    • The PSA loads the specific MPP (in our case the NMP) depending on the logical device holding the virtual machines disk.

    • The NMP calls the associated PSP for the logical device

    • The PSP selects the appropriate path to send the I/O down while taking into consideration any load balancing techniques. The I/O is then queued to the hardware/software initiator, CNA, or HBA depending on the storage transport being used.

    • If the previous step fails, the NMP calls the appropriate SATP to process error codes and mark paths inactive or failed, and then the previous step is repeated.

  • The hardware/software initiator, CNA, or FC HBA transforms the I/O request into the proper form depending on the storage transport (iSCSI, FC, or FCoE) and sends the request as per the PSAs instructions.

    I/O flow from start to finish