Technology | DOI: 10.1145/2063176.2063183
Great strides are being made in finding fast alternatives to the slow disks
that dominate storage systems, but fast media are not nearly enough.
THe GRowTH In the power of computers, driven for de- cades by Moore’s Law and more recently by increased core counts, coupled with
huge improvements in network bandwidth, disk densities, and other metrics, is nothing short of astonishing.
Yet practitioners at the high end say
we are losing the battle against the
“Our society is literally drowning in
data,” notes Allan Snavely, associate
director of the San Diego Supercom-
puter Center at the University of Cali-
fornia at San Diego (UCSD). “Data ac-
quisition devices ranging from space
telescopes to genomic sequencing
machines, and the Internet itself, are
producing data almost faster than it
can be written to disk.”
Indeed, disks are a major part of the
problem. Disk-based storage systems
are 10 to 100 times slower than a net-
work and thousands of times slower
than main memory in delivering data
to an application, in part because the
data comes from a relatively slow elec-
tromechanical device. In recent years,
fast flash memories have begun re-
placing disks in some applications.
And manufacturers have started show-
ing promising prototypes of more ex-
otic non-volatile storage devices such
as phase-change memory (PCM).
While substituting fast media for
slow disks can help, it is by no means
the whole solution. In fact, computer
scientists at UCSD argue that new
technologies such as PCM will hardly
be worth developing for storage systems unless the hidden bottlenecks
and faulty optimizations inherent in
storage systems are eliminated.
A team at UCSD led by Steven Swanson, assistant professor of computer
science and engineering, is doing
just that. A recent prototype, called
a view of the internals of the Moneta storage array with phase change memory modules
Moneta, bypasses a number of functions in the operating system (OS) that
typically slow the flow of data to and
from storage. These functions were
bypasses a number
of functions in the
that typically slow
the flow of data to
and from storage.
developed years ago to organize data
on disk and manage input and output (I/O). The overhead introduced
by them was so overshadowed by the
inherent latency in a rotating disk
that they seemed not to matter much.
But with new technologies such as
PCM, which are expected to approach
dynamic random-access memory
(DRAM) in speed, the delays stand in
the way of the technologies’ reaching
their full potential. Linux, for example, takes 20,000 instructions to perform a simple I/O request.
Moneta is a prototype high-performance storage array. It uses field-programmable gate arrays to implement a scheduler and a distributed
set of memory controllers attached to
conventional DRAM emulating PCM.
(A similar prototype from the same
researchers, called Onyx, uses PCM.)