TR-09-2.pdf
"Understanding intrinsic characteristics and system implications of
flash memory based solid state drives",
Feng Chen, David Koufaty, and Xiaodong Zhang
Proceedings of 2009 ACM SIGMETRICS Conference on Measurement and Modeling
of Computer Systems}, (SIGMETRICS/Performance 2009), Seattle, WA, June 15-19,
2009.
Abstract
Flash Memory based Solid State Drive (SSD) has been called a "pivotal
technology" that could revolutionize data storage systems. Since SSD shares
a common interface with the traditional hard disk drive (HDD), both
physically and logically, an effective integration of SSD into the storage
hierarchy is very important. However, details of SSD hardware implementations
tend to be hidden behind such narrow interfaces. In fact, since
sophisticated algorithms are usually, of necessity, adopted in SSD controller
firmware, more complex performance dynamics are to be expected in SSD than
in HDD systems. Most existing literature or product specifications on
SSD just provide high-level descriptions and standard performance data,
such as bandwidth and latency.
In order to gain insights into the unique performance characteristics of SSD,
we have conducted intensive experiments and measurements on different types
of state-of-the-art SSDs, from low-end to high-end products. We have
observed several unexpected performance issues and uncertain behavior of
SSDs, which have not been reported in the literature. For example, we found
that fragmentation could seriously impact performance by a factor of over
14 times on a recently announced SSD. Moreover, contrary to the common
belief that accesses to SSD are uncorrelated with access patterns, we
found a strong correlation between performance and the randomness of data
accesses, for both reads and writes. In the worst case, average latency
could increase by a factor of 89 and bandwidth could drop to only 0.025MB/sec.
Our study reveals several unanticipated aspects in the performance dynamics
of SSD technology that must be addressed by system designers and
data-intensive application users in order to effectively place it in the
storage hierarchy.