An ephemeral disk is temporary block storage attached to a workload for fast local I/O, then discarded, reset, or reused when that workload ends. Unlike persistent volumes, it is not meant to preserve data across restarts or tenant changes.
In cloud security, ephemeral disks matter because “temporary” does not automatically mean “empty.” If a provider reassigns blocks without proper zeroing, leftover bytes can create data remanence and expose files, metadata, or database fragments to another tenant. Attackers look for these reuse paths, while defenders verify sanitization, encryption, and lifecycle controls such as block zeroing, secure deletion, and validation of storage pools. Proper handling of ephemeral disks is part of tenant isolation and a core defense against cross-customer data leakage.