I was looking at the layout of RAID-5 object configuration the other day, and while these objects were deployed on vSAN with 4 components, something caught my eye. It wasn’t the fact that there were 4 components, which is what one would expect since we implement RAID-5 as a 3+1, i.e. 3 data segments and 1 parity segment. No, what caught my eye was that one of the components had a different vote count. Now, RAID-5 and RAID-6 erasure coding configurations are not the same as RAID-1. With RAID-1, we deploy multiple copies of the data depending on how many…
I recently noticed a blog post describing some very strange behaviors in 2-node and 3-node vSAN clusters. I was especially concerned to read that when they introduced a failure and then fixed that failure, they did not experience any auto-recovery. I have reached out to the authors of the post, just to check out some things such as version of vSAN, type of failure, etc. Unfortunately I haven’t had a response as yet, but I did feel compelled to put the record straight. In the following post, I am going to introduce a variety of operations and failures in my…
In the VSAN 6.0 Design & Sizing Guide, a caveat was placed around the size of a VMDK, and the Number of Failures to Tolerate (FTT) number. It reads like this: “If the VMDK size is greater than 16TB, then the maximum value for NumberOfFailuresToTolerate is 1.” I’m pleased to say that this restriction has been lifted in VSAN 6.2.
One policy setting that I have yet to discuss in any great detail in my blog posts about VSAN. The ForceProvisioning policy setting, when placed in the VM Storage Policy, allows Virtual SAN to violate the NumberOfFailuresToTolerate (FTT), NumberOfDiskStripesPerObject (SW) and FlashReadCacheReservation (FRCR) policy settings during the initial deployment of a virtual machine. This can be useful for many reasons. One reason is that it enables the boot-strapping of a vCenter server on a VSAN deployment as highlighted by William Lam in this excellent blog post on the subject. Another reason is that it allows the provisioning of virtual machines…
Yesterday I posted an article which discussed some common misconceptions with Virtual SAN that come up time and again. Once I published that article, I immediately had an additional question about basic VSAN behaviour and functionality related to stripe width. More specifically, the question is how many disks do you need to satisfy a stripe width requirement. Let’s run through it here.
I’m currently neck-deep preparing for the next version of Virtual SAN to launch. As I prepare for all the new features that are coming (that I hope to be able to start sharing with you shortly), I’m still surprised by the misconceptions that still exist with regards to basic Virtual SAN functionality. The purpose of this post is to clear up a few of those.