Friday, February 18, 2011


I attended USENIX's File And Storage Technologies conference. Here's a brief list of the things that caught my attention:
  • The first paper, and one of the Best Paper awardees, was "A Study of Practical Deduplication" (PDF), an excellent overview of deduplication applied to file systems. It makes available much valuable new data. In their environment whole-file deduplication achieves about 3/4 of the total savings from aggressive block-level deduplication.
  • In fact, deduplication and flash memory dominated the conference. "Reliably Erasing Data From Flash-Based Solid State Drives" from a team at UCSD on revealed that, because flash memories effectively require copy-on-write techniques, they contain many logically inaccessible copies of a file. These copies are easily accessible by de-soldering the chips and thus gaining a physical view of the storage. Since existing "secure delete" techniques can't go around the controller, and most controllers either don't or don't correctly implement the "sanitization" commands, it is essential to use encrypted file systems on flash devices if they are to store confidential information.
  • Even worse, Michael Wei's presentation of this paper revealed that at least one flash controller was doing block deduplication "under the covers". This is very tempting, in that it can speed up writes and extend the device lifetime considerably. But it can play havoc with the techniques file systems use to improve robustness.
  • "AONT-RS: Blending Security and Performance in Dispersed Storage Systems" was an impressive overview of how all-or-nothing transforms can provide security in Cleversafe's k-of-n dispersed storage system, without requiring complex key management schemes. I will write more on this in subsequent posts.
  • "Exploiting Memory Device Wear-Out Dynamics to Improve NAND Flash Memory System Performance" from RPI provides much useful background on the challenges flash technology faces in maintaining reliability as densities increase.
  • Although it is early days, it was interesting that several papers and posters addressed the impacts that non-volatile RAM technologies such as Phase Change Memory and memristors will have.
  • "Repairing Erasure Codes" was an important Work In Progress talk from a team at USC, showing how to reduce one of the more costly functions of k-of-n dispersed storage systems, organizing a replacement when one of the n slices fails. Previously, this required bringing together at least k slices, but they showed that it was possible to manage it with many fewer slices for at least some erasure codes, though so far none of the widely used ones. The talk mentioned this useful Wiki of papers about storage coding.

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