VM Storage Policies and disk space usage

[ADMTim]

We have a storage policy that is called Standard - Data is stored on two hosts while the third host monitors the other two. I want to turn this policy off to gain disk space and us None as the storage policy. However, a colleague says that they are the same and I won't gain disk space by turning off the Standard storage policy. I can't find any documentation to support that. Does anybody know if it is true?

[zdickinson]

Good afternoon, sounds like you want to go from FTT = 1 to FTT - 0.  Seems risky, I'm hoping not important data.  I guess the questions is.  With FTT = 0 does it keep a copy of the data and a witness or two copies of the data.  Good question.  My guess before doing any research is that it would keep one copy of the data and a witness.  So yes, you should see free space rise going to FTT = 0.

Not much, but "With only one copy (FTT=0)" from VMware Virtual SAN Delivers Enterprise Level Availability - VMware vSphere Blog - VMware Blogs

Thank you, Zach.

[ADMTim]

Hello, thank you for your reply and the helpful link. We have a VSAN with HA. Our data is backed up. I also wonder what value the FTT=1 has if it is consuming 1/3 of our VSAN Datastore. Also, we have a cluster and I don't see how to apply different storage policies to individual VM's? So for example if I want some to be FTT=1 and others FTT=0. To me it appears it is all or nothing in a cluster.

[zdickinson]

The value is that you can have a host go down and have the VM keep running.  I'm assuming you have a 3 node cluster.  VM is on host 1, witness on host 2, data on host 3 with FTT = 0.  If host 2 or 3 go down, you won't have quorum and your VM on host 1 will become unresponsive.  You will need to wait for the crashed host to come back online before you can get the VM running.  Assuming you don't have data corruption.  If you did, you would need to go to backup.

It's also handy for maintenance.  How would you install patches on host 2 or 3?

With FTT = 1 You might have VM running on host 1 along with a copy of the data, host 2 with a witness, and host 3 with the second copy of the data.  Now any of the host can crash and you still have quorum.

Agreed on the amount of storage it takes.  In v6 you can do RAID 5/6 which takes up less, but you need more hosts.  If you go all flash vSAN, you get compression and dedupe.

There is a default storage policy.  FTT = 1, stripe width = 1, thin provision, etc...  You need to manually create others.  You can then apply them to VMs, or make it default and then new VMs will get the policy at creation.

Thank you, Zach.