Block zeroing is the practice of overwriting newly allocated storage blocks with zeros before a workload can read them. In thin-provisioned or shared storage systems, the same physical disk blocks may be reused by different tenants, containers, or virtual machines. If those blocks are not cleared first, old data can remain in the unused portions and become visible as data remanence.
It matters because storage hygiene is part of isolation. A network firewall or container boundary may be correct, yet stale bytes can still leak through the block layer if zeroing is skipped or incomplete. Attackers look for these mistakes by reading newly provisioned space and recovering metadata, file fragments, or application content. Defenders prevent this with secure allocation paths, verified zero-on-alloc behavior, encryption, and regular validation of storage systems.