When you bulk copy data into a partitioned table without specifying a partition number, the SAP ASE server randomly assigns each batch to an available partition. Copying rows in a single batch places all those rows in a single partition, which can lead to load imbalance in the partitioned table.
To help keep partitioned tables balanced, use a small batch size when bulk copying data or specify the partition ID during the bcp session. For information about partitioning tables, see the Performance and Tuning Guide.