I was going to make this part 11 of my vSphere 5.5 Storage Enhancements series, but I thought that since this is such a major enhancement to storage in vSphere 5.5, I’d put a little more focus on it. vFRC, short for vSphere Flash Read Cache, is a mechanism whereby the read operations of your virtual machine are accelerated by using an SSD or a PCIe flash device to cache the disk blocks of the application running in the Guest OS of your virtual machine. Now, rather than going to magnetic disk to read a block of data, the data can be retrieved from a flash cache layer to improve performance and lower latency. This is commonly known as write-through cache, as opposed to write-back cache, where the write operation is acknowledged when the block of data enters the cache layer.
This is an interesting announcement for those of you following emerging storage technologies. We’ve been talking about flash technologies for some time now, but for the most part flash has been either an SSD or PCIe device. Well, we now have another format – DIMM-based flash storage device. And VMware now supports it.
For those of you participating in the VMware Virtual SAN (VSAN) beta, this is a reminder that there is a VSAN Design & Sizing Guide available on the community forum. It is part of the Virtual SAN (VSAN) Proof of Concept (POC) Kit, and can be found by clicking this link here. The guide has recently been updated to include some Host Memory Requirements as we got this query from a number of customers participating in the beta. The actual host memory requirement directly related to the number of physical disks in the host and the number of disk groups configured on the host. If you want to know more about disk groups, have a read of an article that I wrote about disk groups on the vSphere storage blog.
I had a customer reach out to me recently to discuss VMware’s Storage I/O Control behavior and Adaptive Queuing behavior and how it works with QLogic’s Execution Throttle feature. To be honest, I didn’t have a good understanding of the Execution Throttle mechanism from QLogic so I did a little research to see if this feature inter-operates with VMware’s own I/O congestion management features.
This is a topic which has been discussed time and time again. It relates to an advanced storage parameter called Disk.SchedNumReqOutstanding, or DSNRO for short. There are a number of postings out there on the topic, without me getting into the details once again. If you wish to learn more about what this parameter does for you, I recommend reading this post on DSNRO from my good pal Duncan Epping. Suffice to say that this parameter is related to virtual machine I/O fairness. In this post, I’ll talk about changes to DSNRO in vSphere 5.5.
All Flash Arrays continue to make the news. Whether it is EMC’s XtremIO launch or Violin Memory’s current market woes, there is no doubt that AFAs continue to generate a lot of interest. Those of you interested in flash storage will not need an introduction to SolidFire. These guys were founded by Dave Wright (ex-RackSpace) and have been around since 2009. I have been trying to catch up with SolidFire for sometime as I’d heard their pitch around Quality of Service on a per volume basis and wanted to learn more, especially how it integrated with vSphere features. Recently I caught up with Dave Cahill and Adam Carter of SolidFire to have a chat about SolidFire in general and what the VMware integration points are.
Before I left for PTO, I wrote an article on a number of different storage vendors you should be checking out at this year’s VMworld 2013. One of these was a new start-up called PernixData. With tongue firmly in cheek, I suggested that PernixData might use VMworld as a launchpad of their FVP (Flash Virtual Platform) product. Well, needless to say, my good friend Satyam Vaghani, CTO at PernixData, reached out to me to say that they were in fact announcing FVP before VMworld. He shared some details with me, which I can now share with you if you haven’t heard about the announcement.