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FAST 2002 Abstract
Selecting RAID levels for disk arrays
Eric Anderson, Ram Swaminathan, Alistair Veitch, Guillermo A. Alvarez and John Wilkes, Storage and Content Distribution Department, Hewlett-Packard Laboratories
Abstract
Disk arrays have a myriad of configuration parameters
that interact in counter-intuitive ways, and those interactions
can have significant impacts on cost, performance,
and reliability. Even after values for these parameters
have been chosen, there are exponentially-many ways to
map data onto the disk arrays' logical units. Meanwhile,
the importance of correct choices is increasing: storage
systems represent an growing fraction of total system
cost, they need to respond more rapidly to changing
needs, and there is less and less tolerance for mistakes.
We believe that automatic design and configuration of
storage systems is the only viable solution to these issues.
To that end, we present a comparative study of a
range of techniques for programmatically choosing the
RAID levels to use in a disk array.
Our simplest approaches are modeled on existing, manual
rules of thumb: they "tag" data with a RAID level before
determining the configuration of the array to which
it is assigned. Our best approach simultaneously determines
the RAID levels for the data, the array configuration,
and the layout of data on that array. It operates as an
optimization process with the twin goals of minimizing
array cost while ensuring that storage workload performance
requirements will be met. This approach produces
robust solutions with an average cost/performance 14–17% better than the best results for the tagging schemes,
and up to 150–200% better than their worst solutions.
We believe that this is the first presentation and systematic
analysis of a variety of novel, fully-automatic RAID-level
selection techniques.
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