@InProceedings{bairavasundaram:x-ray,
  author = {Lakshmi N. Bairavasundaram and Muthian Sivathanu and Andrea C.
  Arpaci-Dusseau and Remzi H. Arpaci-Dusseau},
  title = {{X-RAY}: A non-invasive exclusive caching mechanism for {RAID}s},
  booktitle = {Proceedings of the 31st Annual International Symposium on
  Computer Architecture},
  year = {2004},
  month = {June},
  pages = {176--187},
  institution = {Univ Wisconsin, Dept Comp Sci, Madison, WI 53706 USA},
  publisher = {IEEE Computer Society Press},
  copyright = {(c)2004 Institute for Scientific Information, Inc.},
  address = {Munich, Germany},
  URL = {http://www.cs.wisc.edu/wind/Publications/xray-isca04.html},
  keywords = {RAID, x-ray, caching policies, pario-bib},
  abstract = {RAID storage arrays often possess gigabytes of RAM for caching
  disk blocks. Currently, most RAID systems use LRU or LRU-like policies to
  manage these caches. Since these array caches do not recognize the presence
  of file system buffer caches, they redundantly retain many of the same blocks
  as those cached by the file system, thereby wasting precious cache space. In
  this paper, we introduce X-RAY, an exclusive RAID array caching mechanism.
  X-RAY achieves a high degree of (but not perfect) exclusivity through
  gray-box methods: by observing which files have been accessed through updates
  to file system meta-data, X-RAY constructs an approximate image of the
  contents of the file system cache and uses that information to determine the
  exclusive set of blocks that should be cached by the array. We use
  microbenchmarks to demonstrate that X-RAY's prediction of the file system
  buffer cache contents is highly accurate, and trace-based simulation to show
  that X-RAY considerably outperforms LRU and performs as well as other more
  invasive approaches. The main strength of the X-RAY approach is that it is
  easy to deploy -- all performance gains are achieved without changes to the
  SCSI protocol or the file system above.}
}