I spent some time over the last few months writing an application that I’ve always wanted: a backup verifier. I store backups of my data both on-site and in the cloud. But unless I do a “restore” of everything now and then, how do I know that the backup is actually good? That’s where the backup verifier helps…

The backup verifier scans through the original files and creates a SHA-1 hash of each file. It then compares that SHA-1 hash with each file in the backup. If they don’t match, there’s a problem!

Why SHA-1? Well, we currently use Backblaze B2 for our cloud backups. Backblaze stores a SHA-1 hash with each file. So that allows the backup verifier to compare the SHA-1 hashes without downloading the file.

But how do I know that the file in Backblaze actually matches the SHA-1 hash value? Well, I could just trust Backblaze. But I’d rather not completely rely on that. I don’t have unlimited super-fast internet — so the backup verifier can’t download all the files every time it runs. But it can download some of them. So it picks a random selection of files, downloads them from Backblaze, and then verifies that the hash values are correct. That’s good enough for me.

That’s just one of the features that makes the backup verifier different from a “simple” file comparison app. If I have time at some point, maybe I’ll clean up the application and make it publicaly available in some form…