Lets just say i have an access switch with 8 1G port downlink, and all downlink ports are connected to the users. I want to connect said switch to an aggregation switch.
How do I determine the bandwidth needed for the uplink? Do I need 8x1G= 8G uplink which means a 10G port?
It all depends on your workloads.
If you've got eight "light" users that work with some office documents, surf the 'net, send and receive a few emails, oversubscription is a non-issue. It might not even matter if the users are connected by gigabit or only 100 Mbit/s. You could even have 40 end nodes or more on a single gigabit uplink without any problem.
If you've got eight servers that are moderately-to-seriously frequented, or heavy users (moving large data amounts, video, ...) you'd want to make sure that there are no bottlenecks. Server backup may also run out of its window, so you'd need at least 2-4 Gbit/s uplink, the more the better.
In extreme, you've got a backup repository cluster where you'd want no potential bottleneck at all - that'd mean a 10 Gbit/s uplink (or for that matter, dedicated 10 Gbit/s to each node, 40+ Gbit/s uplink).
To better size your workloads it really helps to monitor the current links for a while. Ideally, you track daily traffic amount and height and width/length of the peaks. At least try to grab (or write down) the port counters once or twice a day.
The correct thing would be to monitor this switch, so you would know how much these users consume today. If you think about expanding this network in this location, I believe that you should think about a switch with SFP+, at first you can use the 1Gbps Ethernet port, if necessary change to SFP+, that way the equipment will serve you for a good time.
Think about how much your network will grow, and how long you want to keep this equipment, good luck! ;P
It's all depends upon your bandwidth utlization and traffic and number of end users connected on access -layer switch it's . With help of Port channel and link aggrigation you can bind 8 uplinks from distribution to access switch or from core switch to access switch ..
