Some senseless babbling from Murray Lesser to Mike Ruskai
on 10-19-99  08:56 about HPFS info quest...

 ML> (Excerpts from a message dated 10-18-99, Mike Ruskai to All)

 ML> Hi Mike--
 
 MR>I'm attempting to gather information on how the size of a drive
 >correlates with the HPFS system area.

 ML> ...much deleted
 
 MR>Is CHKDSK incorrect, or is there something big that I'm missing?

 ML> Download the latest version of the DFSEE utility from your
 ML> friendly BBS and see if that will help you.  Here is a quotation from
 ML> the introduction to the doc file of an early 1999 version (DFSEE294)
 ML> that might give you some ideas as to what is covered in the utility:

 ML> "The DFSee program is a disk and filesystem browser with an emphasis
 ML> on the HPFS and FAT filesystems, disk partitioning and some NTFS.  It
 ML> will support different file-systems sometime in the future. 
[snip]

I downloaded the program (dfsee307.zip), but haven't yet spent the time
to figure out how to use it.

What I did instead was write a program to traverse the freespace bitmaps on
the drive "manually", and count up the free sectors that way.  On every
drive in my system, the result was that DosQueryFSInfo() returned 4096
sectors too few in free space.  The reported free space is firm, however,
when attempting to write to the drive.  The write fails at that value, not
the value computed by tallying the freespace bitmaps.

So it would seem that there's a bug somewhere in the chain that eats 2MB of
space when using HPFS.  The number isn't related to drive geometry, either.
The one drive is addressed with 63 sectors per track, and 64 tracks per
cylinder (heads).  Another is 63 sectors per track, but 16 tracks per
cylinder.

I'd like to release the free space checker for others to use, to see if the
space loss is universal, but I'm not sure how to handle drives greater than
4GB.  The free space bitmap list is four sectors, which is enough room for
4GB worth of free space bitmaps.  There's also a spare bitmap sector list
in the SuperBlock, but I don't know if it's also four sectors long, or if
there's another way to determine its length.  If the former, then yet
another run of free space bitmap locations must be somewhere, else HPFS
would die at 8GB.  That would mean figuring out that sucker's location.  If
the latter, it'd be easier, provided I knew how to determine the length of
the list.

Mike Ruskai
thannymeister@yahoo.com


... As I feared, you have no sense of humor.

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