Featured, Virtualization Software

An Introduction to vSphere 5.5 Flash Read Cache (vFRC)

vSphere 5.5 Flash Read Cache is a brand new feature which is part of vSphere 5.5. Key Features:

  • Hypervisor-based software-defined flash storage tier solution.
  • Aggregates local flash devices to provide a clustered flash resource for VM and vSphere hosts consumption (Virtual Flash Host Swap Cache)
  • Leverages local flash devices as a cache
  • Integrated with vCenter, HA, DRS, vMotion
  • Scale-Out Capability: 32 nodes

Why vSphere Flash Read Cache?

  • Cache is a high-speed memory that can be either a reserved section of main memory or a storage device.
  • Supports Write Through Cache Mode
  • Improve virtual machines performance by leveraging local flash devices
  • Ability to virtualize suitable business critical applications

What is Write-Through?

Write through is a storage method in which data is written into the cache and the corresponding storage location at the same time. The cached data allows for fast retrieval on demand, while the same data on the disk ensures that nothing will get lost if a crash, power failure, or other system disruption occurs.


vSphere Flash Read Cache: Fully Integrated with vSphere

All the management tasks pertaining to the installation, configuration & monitoring of vSphere Flash Read Cache will be done only from the vSphere client:


  • Each host creates a Virtual Flash Resource containing one or multiple flash based devices.
  • There can only be one Virtual Flash Resource per vSphere host.
  • Flash based devices are pooled into a new file system called VFFS.

Three options available to consume the flash

  • Virtual Flash Host Swap Cache (VM transparent cache)
    With VM-transparent caching, the VMs will share a pool of flash resources and are not aware that they are doing so; they will simply benefit from having flash in their I/O path.
    Virtual Flash Host Swap Cache provides the ability to use the Virtual Flash Resource for memory swapping.
  • Virtual Machine Virtual Flash Read Cache (VM-aware Cache)
    With VM-aware caching, chunks of flash can be allocated on a per VM basis, and these will show up as SCSI disks in the Guest OS.
    Block Size configuration capabilities Min 4KB – Max 1M


  • vSphere Host Swap Cache
    Ability to utilize up to 4TB of vSphere Flash Resource for vSphere Flash Swap Caching purposes.Virtual Flash Host Swap Cache configuration is only available via the vSphere Web Client.




vSphere Flash Read Cache Interoperability

  • Fully integrated with vMotion, DRS, and HA.
  • vMotion migration workflows have been modified to include new checkpoints.
  • Advanced settings allows individual VMDK migration settings.