Off by one

I made a small modification to phybs to verify the function of jumpers 7-8 on the WD Advanced Format drives (see here and here). It is supposed to cause the disk to internally shift every write by one sector, so that a write to sector 63 (where the first partition on a PC normally starts) actually goes to sector 64, which coincides with the beginning of a physical 4,096-byte sector. These numbers confirm this:

   count    size  offset    step        msec     tps    kBps
   32768    4096       0   16384       78631      34    1666
   32768    4096     512   16384       79880      33    1640
   32768    4096    1024   16384       73164      36    1791
   32768    4096    1536   16384       77727      34    1686
   32768    4096    2048   16384       76975      35    1702
   32768    4096    2560   16384       74970      36    1748
   32768    4096    3072   16384       79379      34    1651
   32768    4096    3584   16384       28094      96    4665

The firmware on the disk shifts everything forward by 512 bytes, so all these passes are unaligned except the last one, because 3,584 + 512 = 4,096.

Leave a Reply

Your email address will not be published. Required fields are marked *

To create code blocks or other preformatted text, indent by four spaces:

    This will be displayed in a monospaced font. The first four 
    spaces will be stripped off, but all other whitespace
    will be preserved.
    
    Markdown is turned off in code blocks:
     [This is not a link](http://example.com)

To create not a block, but an inline code span, use backticks:

Here is some inline `code`.

For more help see http://daringfireball.net/projects/markdown/syntax