Avaliability in data security means able to tolerate the loss of the data / information in instances of disaster.
Again we can divide avaliability into 3 classes :
Class 1 - Tolerance for loss of data / information for more than a week
Class 2 - Tolerance for loss of data/information for more than a day but less than a week
Class 3 - Tolerance for loss of data / information for less than a day