Thats not entirely correct. Data is indeed not stored in one central place but in instances (node or pods), but it doesnt mean that all data is chunked like that. Good example is email which is also a federated network that works similar to those social networks. This means that just like you are able to send an email form disroot to another address (say, riseup), your diaspora posts are visible to people on different pods. That means that there is no central entity that owns all the data but users can choose their service provider. That however means that most of your data is stored on the originating pod and only things like public posts or direct messages are propagated across the network. Think of it like this: Imagine while on twitter you could check posts from people on facebook and interact with them. This is what federation offers. You can interact wiht people on different servers, run by different people under different rules, as if they were on the same server as you. This allows to create decentralized network of service providers, who by using the same protocol can create a large global network while keeping their autonomy as to how they want their instances to be run, and for whom.
At this moment our diaspora pod has been phased out, meaning you cannot create new accounts anymore. This is because we are focusing on new platform which we will soon add on our webiste as experimental. You can already reach it via https://hub.disroot.org and use your email@example.com as credentials to login. The software we use is called hubzilla and it federates not only with other hubzilla nodes, but also with all zot protocol as well as ActivityPub protocol (eg. mastodon, friendica, pixelfed, peertube, pleroma and many more). It has events, groups and forums built in and fine-grain privacy settings unseen anywhere else on social network ‘market’. It’s still a bit rough around edges UI/UX wise which is something we want to work on, but its usable and it’s been my daily driver for past two years. You can check our disroot community forum at: https://hub.disroot.org/channel/disroot