Storage Policy Based Management Wins

Hey everyone, it’s my first VSAN post! For the past few months I have been building out VSAN on a few test environments. One of them is what I call a Frankenstein cluster. It consists of four Cisco C series hosts with four SSD for Caching and 16 SSD for Capacity set up for an all flash VSAN. In order to do depupe and compression you have to have all flash. I am not going into performance discussions right now, but instead want to talk about Storage Policy Based Management or SPBM. Last week I had someone ask me where to set disk to Thick/Thin within the web client. Notice that Type says “As defined in the VM storage Policy”.

Here is the default policy assigned to this VM. Notice that there is nothing in my rules that would define thick/thin or anything between.

I bet you are now thinking, “What does the Fat Client say”. Well, I am glad you asked. I have a VM on the VSAN datastore with a 40GB Thick Provision Eager Zeroed HD1.

What does that look like for storage usage? I will show both from fat and web client. I think there is a bug in the web client that I will discuss shortly. I bet you are asking why it is showing 80GB Used storage. Remember my storage policy? It is set for raid 1 which will mirror the data. Keep that in mind if you will be using raid 1 with VSAN. Number all seem to jive.


Hey, let’s add a second disk. Let’s make it 100GB Thick Eager Zero. After adding the disk I went into windows and onlined/initialized the disk. After creating the disk in windows…these were the results. This is where I think there is a VMware bug. If you look at the second image, the storage usage in the web client at the VM level never changes. Comparing some numbers. Before the Used total was 591.73GB and this increased to 794.68GB used. This is a change of 203GB. Change in free space went from 6.04TB to 5.84TB which is a change of 200GB. Number looks like what we would expect.

Now let’s have some fun! Time to change the Default VSAN Storage Policy. Go to Homeà VM Storage Policies. Highlight the policy you want to change and then click the little pencil icon to edit. Click the Add Rule drop down at the bottom and choose “Object space reservation (%)”. I chose the default of 0. This means that any disks that have the default storage policy assigned to them will essentially be thin provisioned. Space will not be consumed until something is actually added to the drive. I chose to apply to all VMs now (I only have one). This might take some time if you have a lot of VMs that will change.


You should now be back at the Storage Policy Screen. I want to make sure that policy applied. I clicked on my default storage policy. Once in the policy, I clicked the “Check Compliance” button. On the right side I see “Compliant 1”. Just to make sure this applied to all disks on the VM (you can have separate storage policies apply to different disks) I went back to my VM à Manage à Policies. Notice all disks are compliant.


What does this all mean for my space? Let’s break it down. Used total was 794.68 and now is 514.68. This is a change of exactly 280GB! Free space went from 5.84TB free to 6.11TB. This is a change of 270GB. Look at the used space in the datastore. Notice also that the VM now shows provisioned storage of 144GB and used of 36.43GB.


Now for the interesting part. Let’s look at the fat client. Notice that the disks still show that they are Thick Provision Eager Zeroed, but because of the storage policy, they really are not.

I conclusion the storage policy wins…even though the Fat Client doesn’t seem to know that. Please let me know if you have any questions or want me to test anything else with this scenario.

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