(Solved) vSAN and thin provisioning

[tomas_strand]

Hi everyone!

I'm currently using VSAN for the first time on a three node environment running FTT=1

Object space reservation in the storage policy is set to thin provisioning.

I understand that every VM I migrate to VSAN then takes up double the space. That I understand. What I don't understand is why thin provisioning get's ignored when migrating VM's to VSAN.

For example my vcenter server (thin provisioned) that currently takes up 122 GB in used space ( but has 1,5 TB allocated) would take up 3.9 TB when moved to VSAN.

That's almost all my current VSAN space (4TB)

I'm I missing something? or is this the way it works?

Thank you for any helpful input.

UPDATE: Migration wizard shows space usage based on if the VM was thick provision even though it's thin provisioned. Once migrated it only takes up used space.

[TheBobkin]

Hello Tomas,

Welcome to Communities and vSAN.

"What I don't understand is why thin provisioning get's ignored when migrating VM's to VSAN."

What version of ESXi and vCenter is in use here? VM data (e.g. at the vmdk-primitive level) is thin-provisioned by default on vSAN - in 6.5 and later it doesn't even allow the option when migrating these to be thin-provisioned (again at the vmdk-primitive level) as any thin/thick reservations should be applied via SPBM (e.g. via Storage Policy rules for 'Object Space Reservation').

"For example my vcenter server (thin provisioned) that currently takes up 122 GB in used space ( but has 1,5 TB allocated) would take up 3.9 TB when moved to VSAN."

Where are you seeing that this would take 3.9TB of space? In the Storage vMotion wizard? If so then ensure you are selecting the correct Storage Policy on destination (e.g. vSAN Default Storage Policy if unchanged or whatever OSR=0 policy you have created). If it currently has 122GB written to disk then it *should* use 244GB on vSAN with FTT=1,FTM=RAID1.

"I'm I missing something? or is this the way it works?"

Potentially as this is not the way it is intended to work :smileygrin:

"Do I need to run more hosts to be able to use FTT=5 instead?"

FTT=1,FTM=RAID5 requires a minimum of 4-nodes, an All-Flash configuration and at least vSAN Advanced licensing on the cluster.

Bob

[tomas_strand]

Thank you for replying!

I'm using vSphere 7.0 U1, vSAN 7 U1.

All flash. 12 SSD in total. 3 Cache, 9 Storage

Looks like I was wrong about it taking up 3.9 TB. I was 2.9 TB. Sorry. I have been trying to troubleshoot this for a couple of days and getting tired.

But as you said it should use 244 GB. I have tried changing the VM Storage Policy in the migration wizard. But it doesn't change the amount to anything else then 2.98 TB

[TheBobkin · Accepted solution]

That's a bit odd if it is truly creating them as new thin (at every level) Objects - am I correct in assuming they are thin-provisioned (at the vmdk-level) on source currently?

I do recall some nuisances with space calculation of vMotion wizard being incorrect in some circumstances though I can't recall the specifics, it could just be the wizard being incorrect and they will not use this much space (though if this is the case, this should get fixed by vSphere team) - do you have Advanced Storage vMotion as an option to move a vmdk or two of the vCSA to validate they are indeed landing as thin and not using an inordinate amount of space?

Bob

[tomas_strand]

Yes it looks like it should be thin provisioned. I have also checked the other 15 drives vcenter has attached and they are all thin.

My plan right now is to migrate off the other VM's currently on vSAN.  And then do a clone of vcenter to vSAN to check if the space calculation is wrong.