I have a subsite which is having 130gb of storage. Is it possible to take complete backup of the subsite having content of 130gb? If possible, does we get any issues in doing so?
Yes it is possible but you have to test your options.
export / Import of the subsite will not gonna work as the data is huge and I am sure it will end up timeout error. Another thing, it will take too much times(hours).
Another option is take the Content DB backup and restore. Which means, you have to take the SQL backup of Content DB( in which this subsite). this is quick but this one have a draw back, with this process you cant restore the subsite rather whole site collections.
*note: you can restore the subsite from Content DB but import export with 130Gb will fail.
Another thing you can try 3rd party tools for backup and recovery.
Lastly, i would highly recommend to split the site collection into multiple site collections because this is large enough to restore.