There are quite a few things here;
- Are you sure of your NRI status? There are guidelines as to who is an NRI
- If you are getting salary in India, it is taxable in India
- Any per day allowance you get in Austria, if you have not spent it, its taxable whether you transfer this to India or into NRE or Saving Account is irrelevant. Per Day allowance is meant to cover business expenses while on official work. Any savings of this allowance is treated as additional income.
- Like SKV mentioned, you cannot operate/hold an Savings account if you are NRE.
If you are away for 2.5 Years, you are NRE. Your situation is slightly tricky in the sense that you are getting a salary in India for doing work outside. Please consult a professional CA who can advise you better. If you were not getting an Indian salary, then whatever you earn outside India is non-taxable and you can transfer it into your NRE account. As per regulations an NRI cannot hold a savings account.
Point 3 is more applicable if you are on a short visit.