Keep Your Ebooks Safe
"One preservation network is known under the acronym LOCKSS – Lots of Copies Keeps Stuff Safe – and that’s a good rule of thumb. Always have a backup, and always have multiple backups." LOCKSS
I keep all of my comic book production files on my daily user laptop and backup often to one of these. I also have two more of them, which I keep updated (one is kept in a fireproof safe). I also backup the entire hard drive of the laptop periodically to multiple external drives and burn DVDs annually and keep in the safe.
I don't keep anything on a cloud server, although my website, with all of it's files, are technically on another server. Don't use the cloud for anything proprietary. Google, et al can't be trusted to keep your files safe or private.
Not saying you need to go to these extremes, but, at the minimum, have at least one means of backup and do it often.