Most of the text stored in my DB is from 1MB to 1.5MB big. But not bigger then 1.5MB, because that's the limit I set.
Here are my needs:
A Hash is not revirsable, you can make a 1.5mb large text into a small string with the help of hashing, but you can not make the same hash back into the text.
What you are looking for is a Compression algorithm. You can make the files alot smaller with compression, but unlikely the size of a hash.