vStorage Architecture

The VMware vSphere storage architecture consists of layers of abstraction that hide and manage the complexity and differences among physical storage subsystems.

The Virtual Machine guest operating systems and their applications see the storage as SCSI attached local disks.

In most cases these virtual SCSI disks are files stored in vSphere datastores, but sometimes it is desirable to map block storage directly to virtual machines using Raw Device Mappings (RDM).

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The virtual SCSI disks, or VMDKs, are provisioned as files on vSphere
datastores which may be backed by either local SCSI storage, SAN attached block storage, or NFS NAS storage. The datastore abstraction is a model that assigns storage space to virtual machines while insulating the virtual machine and its guest OS from the complexity of the underlying physical storage technology.

The guest virtual machine is not exposed directly to the Fibre Channel SAN, iSCSI SAN, local storage, or NAS. The storage available to a virtual machine can be extended by increasing the size of the VMDK files.

New virtual disks can be added at any time, but this additional virtual disk
capacity may not be immediately usable without some reconfiguration within the Guest operating system.

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Each vSphere datastore is either a physical Virtual Machine File System
(VMFS) volume on a block storage device or an NFS share on a NAS array.

Datastores can span multiple physical storage subsystems if necessary and a single VMFS volume can contain one or more LUNs from a local SCSI disk, a Fibre Channel SAN disk array, or an iSCSI SAN disk array.

New LUNs added to a physical storage subsystem are detected and can be made available to existing datastores, or used to create new datastores. If the physical storage system supports increasing LUN sizes dynamically, vSphere will recognize this increase in available capacity and it can be used to extend a datastore or create a new datastore if needed. Storage capacity on datastores can be extended using either approach without powering down physical hosts or storage subsystems.

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When more direct access to block storage is required, this can be provided through an RDM. While RDMs bypass the VMFS layer, they are associated with a mapping file that allows vSphere to interact with and manage them in much the same way as VMDKs located in VMFS or NFS Datastores.

The capacity and performance requirements of the VMFS datastores are provided by the
physical capacity of the storage that is connected to the ESXi host, either locally or via a SAN. Similarly, the capacity and performance of the NFS datastores are provided by the NAS systems to which the NFS datastores are mapped.

vSphere 5.5 sees the introduction of VSAN. VSAN provides customers with a distributed compute and storage architecture which is fully integrated and managed by vCenter. At this time it is in public beta and as such is not covered in this course. It should be noted that its introduction will impact how you design and deploy your environment. The diagram shown on this slide does not reflect these changes.

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