S3 compatible means one can point it at any storage that talks S3, which is a lot more flexible than POSIX or NFS.

I have and love my self-hosted immich install. If self-hosted could also use S3 storage, that allows me to use Garage (https://git.deuxfleurs.fr/Deuxfleurs/garage) , which also lets me play games with growable/redundant storage on a pile of second-hand hard drives. IIRC it can only use a mounted block device at the moment, (unless there is a nfs-exposed s3 translator ....)

A lot of existing tooling supports the s3 protocol, so it would simplify the storage picture (no pun intended).

I'm wondering the same thing. He had me until he said "S3".

Likely means S3 compatibility so it can be used with anything, be it a cloud provider or a locally hosted solution like minio

S3-compatible storage. In my case, Backblaze B2. The idea is to make the backend compatible with rclone, so that one can pick whatever storage they want (including B2 / S3 and others)

I backup my immich photos in B2 with rclone but I prefer having it as a separate process (also, the backup is append-only). I don't need "hyperscale", and storing directly on S3/B2/remotely breaks a bit the 3-2-1 rule I want to follow.

On B2 (and S3 storage in general) you can set a retention policy for what happens after you delete an object (e.g: object lock with persistance for at least 30 days). Of course this is not a substitute for a backup - but it's better than discovering that you deleted your whole 1TB library when it's too late