  DNA storage is a promising archival data storage solution to today's big data
problem. A DNA storage system encodes and stores digital data with synthetic
DNA sequences and decodes DNA sequences back to digital data via sequencing.
For efficient target data retrieving, existing Polymerase Chain Reaction PCR
based DNA storage systems apply primers as specific identifier to tag different
set of DNA strands. However, the PCR based DNA storage system suffers from
primer-payload collisions, causing a significant reduction of storage capacity.
This paper proposes using variable strand length, which takes advantage of the
inherent payload-cutting process, to split collisions and recover primers. The
executing time of our scheme is linear to the number of primer-payload
collisions. The scheme serves as a post-processing method to any DNA encoding
scheme. The evaluation of three state-of-the-art encoding schemes shows that
the scheme can recover thousands of usable primers and improve tube capacity
ranging from 18.27% to 19x.
