VMware

Shared storage is a critical enabling technology for a virtualized environment. Shared storage provides the foundation for virtualization spanning multiple servers, enabling services such as VMware vMotionTM, Distributed Resource Scheduler, and VMware vSphere High Availability. In a VMware vSphere environment, customers can deploy shared storage using Network Attached Storage (NAS) or Block based storage (SAN, using Fibre Channel, iSCSI or FCOE). Access to block based shared storage in a VMware vSphere environment is made possible by the VMware Virtual Machine File System (VMFS). VMFS is a high performance cluster file system that allows virtualization to scale beyond the boundaries of a single system. Designed, constructed, and optimized for the virtual server environment, VMFS increases resource utilization by providing multiple virtual machines with shared access to a consolidated pool of clustered storage.

VMFS Resources
Download the VMFS Techncial Overview
(Note: This document is based on vSphere 4.0 and all concepts are relevant to vSphere 5.0. New updates for VMFS in vSphere 5.0 are explained below)

VMFS-5

VMware vSphere 5.0 introduces a new version of VMware’s file system, VMFS-5. VMFS-5 contains many important architectural changes allowing for greater scalability and performance while reducing complexity. While under the covers many fundamental changes have been made the following enhancements are significant from an operational and architectural aspect:

  • 2TB+ Device Support
  • Unified block size
  • Improved sub-block mechanism
  • Additional ATS usage (VAAI Hardware Acceleration for file locking)
VMware vSphere 5.0 allows for a non-disruptive upgrade from VMFS-3 to VMFS-5 ensuring consistency across virtual infrastructures. The unified block size, 1MB, allows for easier deployments and reduced complexity from an architectural and operational aspect while maintaining the scalability and the flexibility that was previously only found with large block sizes. It should be noted that volumes, which are upgraded from VMFS-3 to VMFS-5, would retain their original block size, as modifying the block size would require a reformat of the volume. To allow for greater scalability and to reduce storage overhead associated with small files various enhancements have been made to VMFS-5. These enhancements include optimized sub-block sizes and the allocation of these blocks. These enhancements have resulted in support for large volumes (64TB on a single extent) and higher virtual machine density. The table below depicts the most significant architectural changes for VMFS-5 in comparison to VMFS-3.
Feature VMFS-3 VMFS-5
Support for single extent VMFS volumes larger than 2TB No Yes
Support for Passthrough RDMs larger than 2TB No Yes
Sub-block for space efficiency Yes (64KB, max of ~3k) Yes (8KB max of ~30k)
Small file support No Yes (1KB)
Unified Blocksize No Yes

Table 1. VMFS-5 vs VMFS-3 comparison

Take the Next Step

Find resources and best practices for deploying shared storage for virtual machines.