A system and a method are disclosed that efficiently supports an append operation in an object storage system. A size of data received with a request for an append operation from an application is determined based on a data-alignment characteristic of a storage medium. Data that is not aligned with the data-alignment characteristic is stored in persistent memory and aggregated with other data from the application that is not aligned with the data-alignment characteristic, while data that is aligned with the data-alignment characteristic is stored directly in the storage medium. Aggregated data that becomes aligned with the data-alignment characteristic as additional requests for append operations are received are migrated to the storage medium.