  Currently, Burst buffer has been proposed to manage the SSD buffering of
bursty write requests. Although burst buffer can improve I/O performance in
many cases, we find that it has some limitations such as requiring large SSD
capacity and harmonious overlapping between computation phase and data flushing
phase. In this paper, we propose a scheme, called SSDUP+1. SSDUP+ aims to
improve the burst buffer by addressing the above limitations. First, in order
to reduce the demand for the SSD capacity, we develop a novel method to detect
and quantify the data randomness in the write traffic. Further, an adaptive
algorithm is proposed to classify the random writes dynamically. By doing so,
much less SSD capacity is required to achieve the similar performance as other
burst buffer schemes. Next, in order to overcome the difficulty of perfectly
overlapping the computation phase and the flushing phase, we propose a pipeline
mechanism for the SSD buffer, in which data buffering and flushing are
performed in pipeline. In addition, in order to improve the I/O throughput, we
adopt a traffic-aware flushing strategy to reduce the I/O interference in HDD.
Finally, in order to further improve the performance of buffering random writes
in SSD, SSDUP+ transforms the random writes to sequential writes in SSD by
storing the data with a log structure. Further, SSDUP+ uses the AVL tree
structure to store the sequence information of the data. We have implemented a
prototype of SSDUP+ based on OrangeFS and conducted extensive experiments. The
experimental results show that our proposed SSDUP+ can save an average of 50%
SSD space, while delivering almost the same performance as other common burst
buffer schemes. In addition, SSDUP+ can save about 20% SSD space compared with
the previous version of this work, SSDUP, while achieving 20%-30% higher I/O
throughput than SSDUP.
