A computer program product, according to one embodiment, includes a computer readable storage medium having program instructions embodied therewith. The computer readable storage medium is not a transitory signal per se. Moreover, the program instructions are readable and/or executable by a processor to cause the processor to perform a method which includes: maintaining a first open logical erase block for user writes, and a second open logical erase block for relocate writes. A first data stream having the user writes is received, and transferred to the first open logical erase block. A second data stream having the relocate writes is also received, and transferred to the second open logical erase block. Furthermore, a third data stream is received, and is mixed with the first, second, and/or another data stream in response to determining that an open logical erase block is not available for assignment to the third data stream.