What is VMFS and How Its different from Conventional File Systems

Figure 1 : VMware vSphere Storage Choices

VMFS has always been one of the critical component of Vmware vSphere storage stack as it abstracts the underlying storage and presents it to Virtual Machines in various fomats : virtual disk, passthru RDM, Non-Passthrough RDMs, Snapshots and so on… VMware widely used features like HA, vMotion, Storage vMotion, DRS build up on this Filesystem.

In this blog, we are going to discuss about Basics of VMFS file system, Its features and benefits. Why VMFS is called Clustered file system and how its different from other conventional file systems.

WHAT IS VMFS

VMware Virtual Machine File System is a high performance cluster file system which provides storage virtualization optimized for virtual machines.While conventional file systems allow only one server to have read-write access to the same file system at a given time. VMFS leverages shared storage to allow multiple Vmware vSphere hosts to read and write to the same storage concurrently.

                                Above figure shows how multiple ESX servers with several virtual machines running on them can use VMFS to share a common clustered pool of storage.

VMFS clustering feature provides the foundation for enabling services such as Vmware vMotion, Storage vMotion, High Availability(HA) and Distributed Resource Scheduler (DRS).

FEATURE OF VMFS

• Encapsulation of the entire virtual machine state in a single directory
• Optimization for virtual machines in a clustered environment
• Dynamic datastore expansion by spanning multiple storage extents
• Lock management and distributed logical volume management
• Clustered file system with journal logging for fast recovery

BENEFITS OF VMFS

As an intelligent and automated storage interface for virtual machine (VM) environments, VMFS provides both an automated cluster file system capability and intelligent cluster volume management functions. VMFS has a number of benefits that make it particularly well suited as a cluster file system for the virtual environment.

• Simplify virtual machine provisioning and administration by storing the entire virtual machine state in central location
• VMFS stores all the files that makes up the virtual machine in a single directory or encapsulate entire VM state in a single directory
• It simplifies provisioning and Administration of Vms
• VMFS provides Distributed infrastructure services for multiple ESX servers like HA, DRS, vMotion etc..
• VMFs enabled dynamic growth of datastores by adding multiple extents to it on fly.
• VMFS creates point in time copy of virtual machine data that can be used for testing, backup and recovery operations.
• VMFS is journaling filesystem which recovers virtual machine faster and more reliably in event of server failure with distributed journaling.
• VMFS uses on-disk locking mechanism to make sure a single virtual machine is not powered up on multiple vsphere hosts at a same time.
• It also simplifies disaster recovery using cloning, templates, migration technology.

HOW VMFS IS DIFFERENT FROM CONVETIONAL FILE SYSTEMS

• Conventional file systems allow only one server to have read-write access to the same file at a given time. In contrast, VMFS is a cluster file system that leverages shared storage to allow multiple instances of ESX Server concurrent read and write access to the same storage resources.
• VMFS also has distributed journaling to allow fast and resilient recovery across these multi-server resource pools.
• On-disk locking in VMFS ensures that a virtual machine is not powered on by multiple installations of ESX Server at the same time.
• VMFS also provides the VM snapshot capabilities so necessary for disaster recovery, and is the interface which VMware Data Protection (VDP) leverages to provide proxy backup of virtual environments.

VMFS ARCHITECTURE

a VMFS holds files and has its own Metadata. Metadata gets updated through

• creating a file
• changing a file’s attributes
• powering on a VM
• powering off a VM
• Growing a file

When Metadata is updated, the Vmkernel places a non-persistent SCSI Reservation on the entire of VMFS volume

• lock held on volume for the duration of operation
• Other Vmkernel are prevented from doing metadata updates

HOW TO CREATE & BROWSE VMFS DATASTORE USING vSPHERE CLIENT

Check Out this VMware Video Tutorial on Creating and Browsing VMFS Datastore to store Virtual Machine.

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