Relays no longer keep repositories, so a dead host loses its data unless you kept a backup; Hubble is a public mirror of every repository, funded by a Bluesky grant, with no media and deletions respected, so users can recover and apps can backfill.

Portability needs durability, and the protocol itself does not provide it.

Relays no longer keep a copy of every repository.

So if a host goes dark, its repositories go with it. Apps cannot load the past. Users without their own backup cannot recover.

Hubble is a public mirror of every repository, a library copy of the whole network, synchronised live. Built and run by one developer's project, with a grant from Bluesky.

It stores records, not media. It respects deletions.

Lose your host, and your repository is still there to recover. The protocol made the data portable. A mirror makes it durable.

Check yourself. What does Hubble store, and what does it not?