Selecting RAID levels for disk arrays
Eric Anderson, Ram Swaminathan, Alistair Veitch, Guillermo Alvarez and John Wilkes
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
configura-tion, 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 perfor-mance 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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Last modified: Tue Jul 10 21:36:53 PDT 2001 by Alistair Veitch (aveitch@hpl.hp.com)