question-markSince a major part of my role is creating technical VSAN training for VMware staff and customers i thought it might be useful for me to write up a few questions that I have been asked recently. I will do more posts in the future so you can quickly glance over what some of these answers are.  I will keep the answers short and sweet (just like me).

Question 1 – VM unavailable after network isolation

I have a test VSAN environment with 3 ESXi hosts.  I set a policy to tolerate 1 failure.  I pulled the network cables on one of the esxi hosts.  My VM was still not available after 30 minutes.  Should that happen?  Shouldn’t it still be available?

Answer 1: Yes, If HA is enabled. Please ensure HA is enabled so that the VM can start elsewhere in the cluster.

Question 2 – Resync on boot

Is there anyway to stop a resync operation, or halt it? During VM replicaiton to VSAN, upon powering up VM on VSAN,storage policy takes effect and a resync operation starts.

Answer 2: There is no “recommended” way to stop resync operation as this is an expected process. Interrupting it is unsupported at this time.

Question 3 – Free Space

What is the free space recommendable in VSAN?

Answer 3: The preferred amount of free space in a VSAN disk Group is 30%. The reason this number is used is so that VSAN can move components around under the covers if required and keep the cluster as balanced as possible. This will also help in the event of failures in the cluster from a capacity point of view.

Question 4 – Absent timeout value

If a component is considered absent, does that mean ‘failover’ will not happen for 60 minutes?

Answer 4: From a VSAN point of view a component is said to be ABSENT if VSAN has detected a failure, but VSAN believes that the compact may re-appear (with all data intact). So in other words, an ABSENT state reflects a transient situation that may or not resolve itself over time, and a DEGRADED state is a permanent state. Different events map to these 2 different failure states, and the response to each one is different. Now there is an option to use a command where you can change the timeout value before a rebuild will begin. The command is

esxcli system settings advanced set -o /VSAN/ClomRepairDelay -i

Learn more about this command by using the following Knowledgebase Article 2075456

Question 5 – Migrating to VSAN cluster

Are there any recommendations or best practices to follow when you are migrating VMs from non vSAN to a vSAN cluster?

Answer 5: If both clusters are part of the same vCenter, then this is a straight forward migration back and forth. Best practice is to test your environment first with non-critical and or test VMs first.

Question 6  – Can we do a real-time troubleshooting?

Answer 6 – There are a variety of tools that can be used for real-time troubleshooting. The most common tools are Ruby vSphere Console (RVC), esxcli, esxtop, Performance Service, VSAN Observer. I have also done a 1 hour webinar which can be watched on demand where i cover using some of these tools from a practical point of view. Find the link to that session here

Question 7 – Provisioning to external hosts

Is VSAN capable of provisioning storage to physical servers or only to virtual machines?

Answer 7: In VSAN 6.5 you will be able to provision iSCSI Luns to external hosts. I have wrote a blog post on this, Please take a look here

Question 8 – Controllers

What is the difference between Raid- 0 and Passthrough mode on controllers

Answer 8: Pass thru mode means the disk is passed right to the ESX server and marked as local, this is useful in particular if a disk needs to be replaced so you see the disk instantly once plugged in, With RAID 0 you need to plug in disk and then configure it as a RAID 0 device. To see more detail on this click here

Question 9: Is there an esxcli command I can use to figure out what type of controller is in my ESXi host?

Answer 9: Yes, esxcli storage core adapter list. Below is what the output looks like


Question 10– Learning more

I am new to to VMware so i am so excited to the learn the technologies. Can you give me some suggetions?

Answer 10: Personally I would reccommed taking a look at
as we provide numerous courses in many different formats such as Instructor Led Training along with On Demand Training. We also offer VMware Learning Zone which has hundreds of videos explaining different types of trouble-shooting techniques and much more. Here is the link.

So as i say these are just some of the questions that I have been asked recently and I will do more of these types of topics over the coming months