A data migrating system and method are provided in which a Burst Buffer Network Aggregator (BBNA) process is configured either on the File Servers or on the File System's dedicated I/O nodes to coalesce data fragments stored in participating Burst Buffer nodes under the direction of a primary BB node appointed by a data generating entity prior to transfer of the full data stripe into the File System. The “write” request in the form of a full data stripe is distributed into a plurality of data fragments among participating BB nodes along with corresponding metadata. The primary BB node gathers the metadata from the participating BB nodes, sends the metadata list to the BBNA unit, responsive to which the BBNA unit allocates a buffer sufficient to store the full data stripe, and transfers data fragments from participating BB nodes into the full data stripe buffer, thereby coalescing the data fragments into the full data stripe, which is subsequently transferred from the buffer in the BBNA unit into the File System.