@ChanLK Thanks for reaching out. Can you please confirm my understanding that you already have the azure function which has the output binding that stores the data to the database. Now you have the requirement where you want to store the same data/different data to the storage account that is in different subscription using the same function?
If it is the above case, then you can create the storage account in sub2 and define one more output binding (as you can have multiple output binding) in your azure function in sub1 that uses the connection string of your storage account to store the blob data. For more on storage output binding please refer to this document.