Various embodiments are directed to group-based data storage systems configured for maintaining data exchanged between client devices within channel-specific shards each corresponding with one or more group-identifiers to provide group-based access to those channel-specific shards and for applying group-specific policies for data stored within those channel-specific shards. Membership of particular users within particular groups and within particular channels may be monitored such that access to particular channel shards may be controlled based on group-memberships of the users, and access to data stored within particular channel shards may be controlled based on channel-memberships of the users.