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rm568
Contributor
Contributor
‎06-13-2017 04:47 PM

vSAN 6.6 - RAID-1 Question

All -

I created a 3 Node, ESXi 6.5.0d/vSAN 6.6 cluster and when attempting to add a "Failure tolerance method" to the Virtual SAN Default Storage Policy, I do not see an option to add this rule.  I was expecting to see an option for "RAID-1". 

A case was opened with VMware and they stated that in ESXi 6.5.0d/vSAN 6.6 that the "RAID-1" option is not listed anymore, and that I should only see FTT listed which in this case is FTT1; a vSAN standard license is being used.  With that said, the reason why I have a concern is when I look at the vsan-datastore capacity it's basically the raw disk capacity with no FTT/RAID disk penalty which is 22.62TB.  I was expecting to see about 50% usable space of the raw disk which would be around 11TB.  The one thing that might explain this is the Storage Consumption Model in the Virtual SAN Default Storage Policy states that a virtual disk with a size of 100GB will consume 200GB of disk space.  Will I only see the 2x or 50% disk penalty when I create a VM, and in fact the environment is setup properly with a "RAID-1" configuration?  Thank you.

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TheBobkin
Champion
Champion
‎06-13-2017 05:21 PM

Hello,

Welcome to Communities and vSAN.

Failures To Tolerate=1 (FTT=1) is the same as the configuration of 'RAID1' in that it has two mirrored data components, so technically yes 100GB of disk at the VM-level will use 200GB on vsandatastore.

However this is only going to be the case if all/some VMs are using a proportion of their disk-space or are Thick-provisioned (don't go Thick unless the application/OS benefits from this).

So for example, if you had a Thin-provisioned 100GB vmdk, but the guest OS was only using 50GB, then this will be 50GB+50GB=100GB on vsandatastore.

Thus whether you have Thick or Thin vmdk Objects (VM disks) they will use as much space as they are provided or using (in the case of thin) immediately on creation/migration to vSAN.

Another thing to consider is the extra space that is used by vswp Objects that are the a swap-space the size of the VMs RAM, these can also be configured so that they are Thin-provisioned (they are Thick by default).

Bob

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