i need to replace my current deck that is approx 7 feet about a poured concrete patio. The current deck ledger board is anchored through the house foundation and the deck posts sit on top of the patio anchored with L-brackets. When I replace the deck can I put the posts right on top of the patio or do I need to drill holes in the patio and pour footings.
If you are planning to get a permit, you need to discuss the foundation question with the building inspector. They may allow you to place directly on the slab, they may require testing of the slab to determine if there are footings under the posts, or they may require a new footing under each post.
If you are not planning to get a permit, then the question is what is your basis of design? If you are planning to follow International Residential Code then you need a footing under each post. The required size and depth of footing is discussed extensively in the Prescriptive Residential Wood Deck Construction Guide, available over the internet or perhaps from your building inspector. Footing size and depth is a function of the frost depth, beam and joist span, and soil type.