A couple of weeks ago I posted an article about Virtual Volumes aka vVOLs. This week at VMworld Thomas (Tom) Phelan and Vijay Ramachandran delivered a talk which again addressed this topic but they added Virtual Flash to the mix. The session was “INF-STO2223”.
For those attending Barcelona, sign up for it! It is currently scheduled once on Wednesday at 14:00.
The session started out with a clear disclaimer, this was a technology preview and there is no guarantee whatsoever that this piece of technology will ever be released.
Tom Phelan covered Virtual Flash and Vijay covered Virtual Volumes but as Virtual Volumes was extensively covered in my other blog post I would like to refer back to that blog post for more details on that topic. This blog post will discuss the “Virtual Flash” portion of the presentation, virtual flash or vFlash in short is often also called “SSD caching”.
The whole goal of the Virtual Flash project is to allow vSphere to manage SSD as a cluster resource, just like CPU and memory today. Sounds familiar right for those who read the blog post about vCloud Distributed Storage?! The result of this project should be a framework which allows partners to insert their caching solution and utilize SSD resources more effectively without some of the current limitations.
Virtual Flash may be VM-transparent but also VM-aware. Meaning that it should for instance be possible to allocate resources per virtual machine or virtual disk. Some controls that should be included are reservations, shares and limits. On top of that, it should fully work with vMotion and integrate with DRS.
Two concepts were explained:
- VM transparent caching
- VM-aware caching
VM transparent caching uses a hypervisor kernel caching module which sits directly in the virtual disk’s data path. It can be used in two modes, write thru cache (read only) and write back cache (read and write). On top of that it will provide the ability to migrate cache content during a vMotion or discard the cache.
VM-aware caching is a type of caching where the Virtual Flash resource is presented directly to the virtual machine as a device. This allows the virtual machine to control the caching algorithm. The cache will in this case automatically “follow” the virtual machine during migration. It should be pointed out that if the VM is powered off the cache is flushed.
For those managing virtual environments, architecting them or providing health check services… think about the most commonly faced problem, yes that typically is storage performance related. Just imagine for a second having a caching solution at your disposal which could solve most of these problems…. Indeed that would be awesome. Hopefully we will hear more soon!