Hello Mustafa,
only two physical devices can be connected to form an SVL pair like it happens in VSS with C6500, C6800 and C4500X switches.
Look at the following whitepaper about SVL
https://www.cisco.com/c/dam/en/us/products/collateral/switches/catalyst-9000/nb-06-cat-9k-stack-wp-cte-en.pdf?dtid=osscdc000283
see pag 6 of the above
>> The StackWise Virtual link, formed as an EtherChannel interface, can comprise links ranging from one to eight physical member ports. These links carry two types of traffic: the StackWise Virtual control traffic and normal data traffic
So you should be able to use 10GE links to form the SVL link but you need to use at least two for redundancy.
You need also to add at least one Dual active detection link see table 1 on pag 8.
The dual active detection link provides a way to understand if the supervisors are alive on the two chassis and in case of failure of the stackwise bundle it avoids to have both chassis to go active that will create problems in the network.
Up to 8 stackwise virtual links and up to 4 dual active detection links are supported on C3850.
For dual active detection GE interfaces are enough.
Hope to help
Giuseppe
