A void warren was the term used by the alien civilisation known as Grubs for their interstellar starships.
A "void warren" was controlled by a central giant grub. The grub controlled the actions of the ship, and the army of "helper" grubs (smaller versions of the giant grub). Both the helper grubs and the ship appeared to be extensions of the one main grub (e.g. when a worker grub is hurt, the cry of pain comes from the main grub).
Nothing in a void warren was wasted, and any grubs that were killed or injured were immediately dissolved and re-made into healthy new grubs or re-built into the ship itself.
The technology behind void warrens was of very old origin, the Grubs having developed interstellar flight some 200 million years before humanity. Since then, they were attacked and pursued by the Inhibitors, forcing the nomadic remnants of their civilisation to adopt various methods of hiding themselves, as well as developing new technologies or trading them with other civilisations. Some of these innovations incorporated into void warrens included faster-than-light communication and Inertia-suppression Machinery, gained from the Nestbuilders and the Jumper Clowns. The Grubs also used highly sophisticated force-field technology to help defend their void warrens.
During his development and writing of the novel Chasm City in the early 2000s, Alastair Reynolds did several sketches of the technologies involved in the story. These included two sketches of a Grub "void warren" starship: