Aimed for those who use medium sized storage for virtualization loads, Virsto will add quite a bit of needed functionality to Hyper-V to reduce disk space requirements, improve general disk IO performance, as well as provide faster high availability failover. The disk space saving Linked Clone technology available for VMware ESX and ESXi has been missing from Hyper-V. Virsto provides this.
Virsto in essence provides an intelligent disk cache technology to Hyper-V that when disks are created links to a golden image previously created. The idea behind Virsto is that up to 80% of a golden image stays the same between like virtual machines. The cloning technology of Virsto in essence creates a linked clone for those blocks. Any new blocks written (even overwriting ‘cloned’ blocks) are placed within the new disk container. The disk cloning technology will provide quite a bit of disk savings as long as the cloned disk does not change very much from the golden image. Virsto does not allow you to patch the golden image and have all children of that golden image also be patched. Instead, you are still required to patch each individual virtual machine which could lead to less and less of the golden image being available to an individual VM. Over time the 80% number may fall to 60% or less, yet that still provides a great savings in disk space.
The Virsto approach to disk caching reduces the amount of random IO made by a virtual machine, and instead uses a log file approach similar to databases to serialize writes and therefore speed up disk IO as seen by the virtual disk, and in fact as seen by the physical hardware involved. Virsto is disk, LUN, array, SAN, NAS agnostic and will work with them all. Virsto in effect keeps the heads of your disk from jumping all over the place (what Virsto refers to as the IO Blender), instead they are serialized, which is always a faster way to perform disk IO.
To gain this benefit there are no changes necessary to the virtual machine, a driver is installed within Hyper-V and Virsto takes control of all disk IO from all VMs. Whether 1 or many, the disk IO for all VMs is serialized and the cache allows a consistent disk IO for all VMs, not just one.
Virsto provides disk caching and linked clone style technology for use with Hyper-V, which are missing from the base Hyper-V product. While Virsto is targeting the midrange market, another use case could be the desktop virtualization market. Whether this style of product will be available for VMware ESX or Citrix XenServer is still to be seen.
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