* /usr/src/linux/Documentation/iostats.txt
{{{
On 2.4 you might execute "grep 'hda ' /proc/partitions". On 2.6, you have
a choice of "cat /sys/block/hda/stat" or "grep 'hda ' /proc/diskstats".
}}}
{{{
2.6 diskstats:
   3    0   hda 446216 784926 9550688 4382310 424847 312726 5922052 19310380 0 3376340 23705160

Field  1 -- # of reads issued
    This is the total number of reads completed successfully.
Field  2 -- # of reads merged, field 6 -- # of writes merged
    Reads and writes which are adjacent to each other may be merged for
    efficiency.  Thus two 4K reads may become one 8K read before it is
    ultimately handed to the disk, and so it will be counted (and queued)
    as only one I/O.  This field lets you know how often this was done.
Field  3 -- # of sectors read
    This is the total number of sectors read successfully.
Field  4 -- # of milliseconds spent reading
    This is the total number of milliseconds spent by all reads (as
    measured from __make_request() to end_that_request_last()).
Field  5 -- # of writes completed
    This is the total number of writes completed successfully.
Field  7 -- # of sectors written
    This is the total number of sectors written successfully.
Field  8 -- # of milliseconds spent writing
    This is the total number of milliseconds spent by all writes (as
    measured from __make_request() to end_that_request_last()).
Field  9 -- # of I/Os currently in progress
    The only field that should go to zero. Incremented as requests are
    given to appropriate request_queue_t and decremented as they finish.
Field 10 -- # of milliseconds spent doing I/Os
    This field is increases so long as field 9 is nonzero.
Field 11 -- weighted # of milliseconds spent doing I/Os
    This field is incremented at each I/O start, I/O completion, I/O
    merge, or read of these stats by the number of I/Os in progress
    (field 9) times the number of milliseconds spent doing I/O since the
    last update of this field.  This can provide an easy measure of both
    I/O completion time and the backlog that may be accumulating.

   3    1   hda1 35486 38030 38030 38030

Field  1 -- # of reads issued
    This is the total number of reads issued to this partition.
Field  2 -- # of sectors read
    This is the total number of sectors requested to be read from this
    partition.
Field  3 -- # of writes issued
    This is the total number of writes issued to this partition.
Field  4 -- # of sectors written
    This is the total number of sectors requested to be written to
    this partition.

}}}