VSAN resync behaviour when failed component recovers

I had this question a number of times now. Those of you familiar with VSAN will know that if a component goes absent for a period of 60 minutes (default) then VSAN will begin rebuilding a new copy of the component elsewhere in the cluster (if resources allow it). The question then is, if the missing/absent/failed component recovers and becomes visible to VSAN once again, what happens? Will we throw away the component that was just created, or will we throw away the original component that recovered?

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A closer look at Primary Data

primaryDataPrimary Data were one of the storage vendors that I wanted to catch up with at VMworld 2015. I was fortunate enough to meet with Graham Smith who is their Director of Virtualization Product Management. Graham gave me a demonstration of the Primary Data product in the Solutions Exchange at VMworld, and I also had an opportunity to visit their offices in Los Altos during a recent trip to the bay area and catch up once again with Graham and Kaycee Lai, SVP of Product Management & Sales at Primary Data. Before we get into the product and solution details, I wanted to go over a brief history of the company and the problem that they are trying to solve with their DataSphere Platform.

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Read locality in VSAN stretched cluster

Many regular readers will know that we do not do read locality in Virtual SAN. For VSAN, it has always been a trade-off of networking vs. storage latency. Let me give you an example. When we deploy a virtual machine with multiple objects (e.g. VMDK), and this VMDK is mirrored across two disks on two different hosts, we read in a round-robin fashion from both copies based on the block offset. Similarly, as the number of failures to tolerate is increased, resulting in additional mirror copies, we continue to read in a round-robin fashion from each copy, again based on block offset. In fact, we don’t even need to have the VM’s compute reside on the same host as a copy of the data. In other words, the compute could be on host 1, the first copy of the data could be on host 2 and the second copy of the data could be on host 3. Yes, I/O will have to do a single network hop, but when compared to latency in the I/O stack itself, this is negligible. The cache associated with each copy of the data is also warmed, as reads are requested. The added benefit of this approach is that vMotion operations between any of the hosts in the VSAN cluster do not impact the performance of the VM – we can migrate the VM to our hearts content and still get the same performance.

round-robin-readsSo that’s how things were up until the VSAN 6.1 release. There is now a new network latency element which changes the equation when we talk about VSAN stretched clusters. The reasons for this change will become obvious shortly.

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VSAN 6.1 New Feature – Handling of Problematic Disks

The more observant of you may have observed the following entry in the VSAN 6.1 Release Notes: Virtual SAN monitors solid state drive and magnetic disk drive health and proactively isolates unhealthy devices by unmounting them. It detects gradual failure of a Virtual SAN disk and isolates the device before congestion builds up within the affected host and the entire Virtual SAN cluster. An alarm is generated from each host whenever an unhealthy device is detected and an event is generated if an unhealthy device is automatically unmounted. The purpose of this post is to provide you with a little bit more information around this cool new feature.

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A closer look at Datrium

datriumDatrium are a new storage company who only recently came out of stealth. They are one of the companies that I really wanted to catch up with at VMworld 2015. They have a lot of well-respected individuals on their team, including Boris Weissman, who was a principal engineer at VMware and Brian Biles of Data Domain fame. They also count of Diane Green, founder of VMware, among their investors. So there is a significant track record in both storage and virtualization at the company.

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My VMworld Session – VSAN POC – now available

vsan_stretch_graphic_v02_300dpi_01_square140One of the break-out sessions that I presented at VMworld 2015 on Virtual SAN (VSAN) has been recorded and is now available on YouTube. I co-presented “STO4572 Conducting a Successful Virtual SAN Proof of Concept” with Julienne Pham of VMware, who did the initial part of the session. Julienne explains the planning phase, the kinds of things you need to think about, the conversations that need to take place within the organization and especially the IT team, and then what tools you have available to help you deliver the VSAN Proof Of Concept. I come on stage later on to give you the five typical tests/steps that you need to run through to validate that everything is working on Virtual SAN as expected. Hope you enjoy it.

A brief overview of the new Virtual SAN 6.1

captain-vsanWith the announcements just made at VMworld 2015, the embargo on Virtual SAN 6.1 has now been lifted, so we can now discuss publicly some of the new features and functionality. Virtual SAN is VMware’s software-defined solution for Hyper-Converged Infrastructure (HCI). For the last number of months, I’ve been heavily involved in preparing for the Virtual SAN 6.1 launch. What follows is a brief description of what I find to be the most interesting and exciting of the upcoming features in Virtual SAN 6.1. Later on, I will follow-up with more in-depth blog posts on the new features and functionality.

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