vSphere 6.0: Understanding iSCSI Storage (Part-2)

This series of posts is to cover storage concepts and its configuration. Storage is one of the important features of configuring and managing your virtual environment. Storage options give the flexibility to set up your storage based on your cost, performance, and manageability requirements. Shared storage is useful for disaster recovery, high availability, and moving VMs from one host on another.

In pervious post of this series, we’ve discussed some basics of shared storage, storage protocols, datastores, file systems i-e VMFS, NFS, and vSAN. If you missed previous post of virtual storage series, you can follow:

  1. Understanding Virtual Storage

In this post, we’ll learn about basic concept of iSCSI storage, its components, iSCSI addressing, and iSCSI initiators.

iSCSI Storage

An iSCSI SAN consists of an iSCSI storage system, which contains one or more storage processors. TCP/IP protocol is used to communicate between host and storage array.

iSCSI Components

iSCSI initiator is configured with the ESXi host. iSCSI initiator can be a hardware based either dependent or independent and software based known as iSCSI software initiator.

iSCSI commands are transmitted by the iSCSI initiator over the IP Network, and target receives the SCSI commands from the IP Network. Your virtual environment can have multiple initiators and targets.

An initiator exists in ESXi host while targets exist in storage arrays that are supported by ESXi host. iSCSI arrays use various mechanisms including IP address, subnets, and authentications, to restrict access to targets from hosts.

                                                                  Figure: Thanks to VMware

iSCSI Naming Conventions

The main addressable and discoverable entity is iSCSI node. iSCSI can either be an initiator or target. iSCSI node requires a name so that storage can be managed regardless of address. iSCSI names are formatted in two different ways: the iSCSI qualified name (IQN), and extended unique identifier (EUI).

The most common is the iqn format. iSCSI qualified name (iqn) format iqn.yyyy-mm.naming-authority:unique name, iqn.1998-01.com.vmware.iscsi:name22, where,

  • yyyy-mm is the year and month when the naming authority was established.
  • The name indicates that the vmware.com domain name was registered in January of 1998.
  • Unique name is any name you want to use, for example, the name of your host.

EUI naming convention:

The prefix “eui” followed by 16-chars name that included 24 bits of company name assigned by the IEEE and 40 bits for a unique ID.

Example: eui.16hexdigits ie eui.0123456789ABCDEF

iSCSI Target Name

                                                          Figure: Thanks to VMware

iSCSI Initiators

ESXi hosts use iSCSI initiators to access iSCSI targets. SCSI commands are encapsulated by iSCSI initiators into data packets and enable ESXi host to communicate with iSCSI target

Two types of iSCSI initiators are being used:

  1. Hardware iSCSI initiator – a special purpose adapter capable of accessing an iSCSI target device over TCP/IP network. All iSCSI processing from initiator to target is done by the adapter itself. Hardware iSCSI initiators are further divided into two categories:
  • Depended hardware iSCSI adapter– an adapter that performs the iSCSI processing itself but depends on the VMkernel for accessing the TCP/IP network.
  • Independed hardware iSCSI adapter– an adapter that performs both the iSCSI processing and network functionality itself. This type of adapter implements its own interfaces for networking, configuration, and management and does not depend on VMkernel.
  1. software iSCSI initiator– the initiator code that is built into the VMkernel. The iSCSI SAN device can be accessed using standard network adapters. With the software iSCSI initiator, you don’t need to purchase a hardware iSCSI adapter to obtain iSCSI connectivity, but all iSCSI processing is done by the ESXi host.

independent hardware iSCSI adapter

                                                                    Figure: Thanks to VMware

In my home lab, I’ll also use software iSCSI adapter with VMKernel configurations for IP Storage.

I hope you enjoyed reading this post, if you have any query feel free to comment below. Thanks for reading, and share it to social media if you feel worth sharing it. Be friendly and sociable.

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