vSAN Datastore - what happens when it fills up??

[martinriley]

I understand that vSAN aggregates all your magnetic disk capacity into one big fat datastore, so what happens when this fills up- does it kill all the running VMs as it would normally?  If so is there anything that can be done to protect say, a virtual vCenter server from this?

Cheers!

[depping]

ESXi will never kill VMs... It will stun the VMs which require additional blocks beyond what is available. However, VSAN is smart enough to start moving components from one disk to the other (across hosts when needed) when a disk is looking to fill up.

[depping]

Also, you can reserve space for a given VM upfront. So you can create a policy for vCenter Server for instance with a 100% space reservation.

[martinriley]

Sorry yes I didn't mean 'kill' in the literal sense!

So with the space reservation, this will keep a VM up and running if the total capacity of the vSAN datastore is reached?  Will VMs without a reservation that is larger than it's currently using be stunned at this point?

Also I was at vForum in London yesterday where they were talking about how with a 32-node vSAN cluster you could get up to 4.4Pb of space- but with only one datastore per cluster this will be limited to 64Tb surely?

[depping]

martinriley wrote:

Sorry yes I didn't mean 'kill' in the literal sense!

So with the space reservation, this will keep a VM up and running if the total capacity of the vSAN datastore is reached?  Will VMs without a reservation that is larger than it's currently using be stunned at this point?

Also I was at vForum in London yesterday where they were talking about how with a 32-node vSAN cluster you could get up to 4.4Pb of space- but with only one datastore per cluster this will be limited to 64Tb surely?

1) VMs with a space reservation will have that space "carved" out for them already, so they would keep running. Other VMs may get stunned indeed when they require more disk space. However as stated when a disks reaches, 80% I believe, VSAN will rebalance.

There is no 64TB limit. The 64TB limit is on a VMFS5 volume. But a VSAN datastore is not one monolithic VMFS datastore... So no need to worry

[martinriley]

Ah okay, that makes sense.

One more- so will vSAN also move stuff around to keep the available space contiguous, like HA/DRS does with compute resources, or will it happily span a vmdk across physical disks?

Thanks for your help Duncan

[depping · Accepted solution]

With VSAN a disk is an object. An object exists of multiple components. A component sits on a disk. However VSAN can have 1 VMDK which is an object consisting of multiple components. Those components can cross physical disks, disk groups and even hosts if needed. So there is a lot of room for flexibility.