What kind of data does the disk test read/write?
The standard read test creates a file of 512MB, all other standard disk test create files 200MB in size. The file is filled with data that has a randomness of about 20% before the test begins. The randomness is seeded and is the same every time.
All reads and writes are done in 32kb blocks
Any data written once the tests commence is also roughly 20% random and seeded in the same manner.
If the drive has NTFS compression turned on, PerformanceTest will still try to use an uncompressed file for the standard tests. If it can't create a file in a uncomprssed state, the test will fail.