Optimized pre-copy calibration of hard drives

ABSTRACT

In certain contexts a small window of time exists during which law enforcement has access to a hard-drive suspected of containing important information. Given legal authority to copy or seize this disk, a decision must be made whether to use that access time to make a copy of the disk (which may take more than an hour, depending on the size of the disk) and leave its owner unaware that it has been copied. The copying operation uses especially fast drivers that bypass normal error correction mechanisms. Therefore, for the copy to be successful it is necessary that the disk onto which the copy is placed yield exactly the same bits on subsequent reads as would the original disk. To gain confidence that the copy will be successful the copying software typically chooses some sectors at random, copies them, and determines whether their copies are identical to the original. We address the problem of quantifying the conditional probability that the disk will copy correctly given that some samples have copied correctly, as a function of the, number and placement of those samples. Our framework allows us then to choose the placement of those samples in such a way that this conditional probability is maximized.

INDEX TERMS

Primary Classification:
  C. Computer Systems Organization
  C.4 PERFORMANCE OF SYSTEMS

Additional Classification:
  C. Computer Systems Organization
  C.5 COMPUTER SYSTEM IMPLEMENTATION
      C.5.m Miscellaneous

  K. Computing Milieux
  K.5 LEGAL ASPECTS OF COMPUTING
      K.5.1 Hardware/Software Protection

General Terms:
Performance, Theory