eddy_chong
Contributor
Contributor

VSAN Cluster - Hosts with different number of disk groups

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is it possible to mix different host that each has a different number of disk groups in the same VSAN cluster?

I

Example:

Existing VSAN cluster with 3 x R640 (Only 4 drive slots, assuming 2 disk groups). Get 2 new R740XD which can have up to 32 drives slot, can have more than 2 disk group.

Let say we plan to create 4 disk groups for R740xd.


Can we join R740xd nodes into the existing R640 VSAN cluster (2 disk groups per host only)?

Thanks

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TheBobkin
VMware Employee
VMware Employee

Hello Eddy,

"is it possible to mix different host that each has a different number of disk groups in the same VSAN cluster?"

Yes it is *possible* however it is not advised to have non-homogenous nodes in a cluster - one of the reasons for this is that if one node has for instance 40TB attached as capacity-tier and another only has 10TB, you could be 100% full on one nodes disks while the larger one is only 25% with the same amount of data on each. vSAN will of course attempt to relocate data off disks once they hit 80% full (default setting) but in your scenario it will be very lop-sided. Other things to consider - If you had 3 nodes with 10TB each and 1 node with 40TB, if the 40TB nodes fails you won't have any hope of being able to rebuild all data to FTT=1 and probably cause the remaining nodes to approach being completely out of space resyncing the data it can fit. Space to compute resource ratios would also be non-uniform if you configured it like this.

Bob

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TheBobkin
VMware Employee
VMware Employee

Hello Eddy,

"is it possible to mix different host that each has a different number of disk groups in the same VSAN cluster?"

Yes it is *possible* however it is not advised to have non-homogenous nodes in a cluster - one of the reasons for this is that if one node has for instance 40TB attached as capacity-tier and another only has 10TB, you could be 100% full on one nodes disks while the larger one is only 25% with the same amount of data on each. vSAN will of course attempt to relocate data off disks once they hit 80% full (default setting) but in your scenario it will be very lop-sided. Other things to consider - If you had 3 nodes with 10TB each and 1 node with 40TB, if the 40TB nodes fails you won't have any hope of being able to rebuild all data to FTT=1 and probably cause the remaining nodes to approach being completely out of space resyncing the data it can fit. Space to compute resource ratios would also be non-uniform if you configured it like this.

Bob

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eddy_chong
Contributor
Contributor

Dear Bob,

Thanks for your answer. It definitely answered my question. Ya, I thought of it might not be advisable to do this because of the imbalanced performance; I've overlooked the capacity and rebuild risks.

Initially, I thought I've seen somewhere stated the hosts within the same VSAN cluster need to be the same configuration including the number of disk groups or disk slots but I couldn't find it.

In short, I will say it is a NO for this kind of configuration.

Thanks again.

Eddy

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