CoreData reserve space

Is there some way to reserve the disk space for CoreData object? I need to make sure that application will be constantly able to save data up to 1GB of storage using CoreData model. I know I can check the free space before starting, but this is not enough. This process takes a lot of time, and I need to make sure, that space is reserved at all the time. Model object consists of an array with a lot of measurements that are being added while application is running. I was thinking about creating a lot of empty objects with some flag telling if it's a real data or a placeholder, but it's taking way too long, and app crashes. Any way to preserve the disk space otherwise?