Virtual Machine File System (VMFS)
Increase Storage Flexibility with Shared Storage
VMware vSphere VMFS is a high-performance cluster file system 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.
- Simplify virtual machine provisioning and administration by storing the entire virtual machine state in a central location.
- Create a point-in-time copy of virtual machine data that can be used for testing, backup and recovery operations.
- Support unique virtualization-based capabilities, such as live migration of running virtual machines from one physical server to another, automatic restart of a failed virtual machine on a separate physical server and clustering virtual machines across different physical servers.
- Add virtual disk space to a running virtual machine to increase available resources or for backup.
- Recover virtual machines faster and more reliably in the event of server failure with distributed journaling.
Seamlessly Manage Virtual Machine Storage
VFMS lets you provide adequate storage for virtual machines and plan for future storage needs with minimal administrator effort or intervention.
- Add or delete a vSphere host from a VMFS volume without disrupting other hosts.
- Create new virtual machines without relying on a storage administrator.
- Grow VMFS volumes on the fly.
- Simplify storage management with automatic discovery and mapping of LUNs to a VMFS volume.
Deliver High Performance and Scalability
Central, shared storage of virtual machines with VMFS provides more control, flexibility and performance in managing your virtualized IT environment.
- Store and access the entire virtual machine state from a centralized location.
- Use large block sizes favored by virtual disk I/O. Uses sub-block allocator for small files and directories.
- Connect up to 64 vSphere hosts to a single VMFS volume.
- Support single volumes up to 64TB.
- Run even the most data-intensive production applications such as databases, ERP and CRM in virtual machines.
- Benefit from enhanced VMFS performance with volume, device, object and buffer caching.
You can deploy a VMFS datastore on any SCSI-based local or networked storage device, including Fibre Channel, Fiber Channel over Ethernet (FCoE) and iSCSI SAN equipment.
VMFS is the default storage management interface for block-based disk storage (local and SAN attached). VMFS allows multiple instances of vSphere servers to access shared virtual machine storage concurrently. It also enables virtualization-based distributed infrastructure services such as VMware vSphere Distributed Resource Scheduler, VMware vSphere High Availability, VMware vSphere vMotion and VMware vSphere Storage vMotion to operate across a cluster of vSphere servers. In short, VMFS provides the foundation that enables virtualization scaling beyond the boundaries of a single system.
VMFS uses on-disk locking to make sure a single virtual machine is not powered up on multiple vSphere hosts at the same time. When vSphere HA is enabled, if a server fails, the on-disk lock for each virtual machine is released under control of vSphere HA, allowing the virtual machine to be restarted on other vSphere hosts.
Upgrading from VMFS 3
vSphere 5.5 and up 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 operational complexity while maintaining 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 volume reformat.
For greater scalability and reduced storage overhead associated with small files, various VMFS-5 enhancements have been made. These enhancements include optimized sub-block sizes and the allocation of these blocks, resulting in support for large volumes (64TB on a single extent) and higher virtual machine density.