vsphere-esxi-vcenter-server-55-storage-guide

Introduction to Storage 1This introduction describes available storage options for ESXi and explains how to configure your host sothat it can use and manage different types of storage.This chapter includes the following topics:• “Storage Virtualization,” on page 13• “Types of Physical Storage,” on page 14• “Target and Device Representations,” on page 17• “Storage Device Characteristics,” on page 18• “Supported Storage Adapters,” on page 20• “Datastore Characteristics,” on page 21• “How Virtual Machines Access Storage,” on page 23• “Comparing Types of Storage,” on page 24Storage VirtualizationESXi provides host-level storage virtualization, which logically abstracts the physical storage layer fromvirtual machines.An ESXi virtual machine uses a virtual disk to store its operating system, program files, and other dataassociated with its activities. A virtual disk is a large physical file, or a set of files, that can be copied, moved,archived, and backed up as easily as any other file. You can configure virtual machines with multiple virtualdisks.To access virtual disks, a virtual machine uses virtual SCSI controllers. These virtual controllers includeBusLogic Parallel, LSI Logic Parallel, LSI Logic SAS, and VMware Paravirtual. These controllers are the onlytypes of SCSI controllers that a virtual machine can see and access.Each virtual disk resides on a vSphere Virtual Machine File System (VMFS) datastore or an NFS-baseddatastore that are deployed on a physical storage. From the standpoint of the virtual machine, each virtualdisk appears as if it were a SCSI drive connected to a SCSI controller. Whether the actual physical storagedevice is being accessed through parallel SCSI, iSCSI, network, Fibre Channel, or FCoE adapters on the hostis transparent to the guest operating system and to applications running on the virtual machine.In addition to virtual disks, vSphere offers a mechanism called raw device mapping (RDM). RDM is usefulwhen a guest operation system inside a virtual machine requires direct access to a storage device. Forinformation about RDMs, see Chapter 17, “Raw Device Mapping,” on page 155.VMware, Inc. 13