Comment 3 for bug 912259

Magnus -

     Thanks for the information update! Obviously, the author(s) of the
program focused on hard disk technology as their target environment, rather
than considering the expanded number of other types of storage devices - an
understandable situation. My temporary workaround is to use v.1 of the
program - it does not do the size check for available space on the target SD
card that versions .3 and above do. If you use a partition manager to
de-allocate some space on the SD card (I use the difference between what
Win32 Disk Imager reports as the image size and what Windows reports as the
capacity of the device, plus a little extra), and then capture the image,
the resulting image captured still reports the same size as I reported
previously (too large for an identical SD card), but v.1 of the program
happily writes the image to that SD card until it runs out of space. Since
that "lost" part of the image has no meaning, what is not written doesn't
matter. So far, that seems to be working for me when capturing and image
from an SD card and writing that image back to an identically-sized SD card
as a backup. Obviously not the perfect solution, but it works in that
particular set of circumstances.

     There's a very active community to create an Android CyanogenMod
external boot card for the Nook Color; Win32 Disk Imager is one of the
recommended tools used in the process of creating the card, and there are a
lot of problems reported when trying to make a backup SD card image that can
be written to an identically-sized SD card once the image building process
is complete. You can write the Win32 Disk Imager image to a larger-sized
card, of course, but that workaround is more expensive, and if you create an
image for a 32GB SD card (the maximum size card that the Nook Color will
accommodate), you're out of luck backing it up unless you use the workaround
I described above.

     Again, thanks for your attention to this issue and your efforts! I'll
post the information (crediting you, of course) and the workaround to the
various forums that support the Nook 2 Android CyanogenMod process.

Regards,
Dennis

----- Original Message -----
From: "Magnus Karlsson" <email address hidden>
To: <email address hidden>
Sent: Wednesday, February 15, 2012 10:45 AM
Subject: [Bug 912259] Re: Win32 Disk Imager Creates an .IMG file that is
toobig to restore to identical media

See Bug #932321: getNumberOfSectors() returns incorrect number

The program is using an incorrect way to figure out the raw device size.
The correct way is to ask for the partition size of the raw disk rather
than trying to use the disk geometry information (like cylinders,
tracks/cylinder, sectors/track) to figure out the device size since
those numbers are just made up by windows to give an approximation of
the disk size. There is no size information on the SD card about
"cylinders" or "tracks" etc, just the raw block count (1 block = 512
bytes = 1 "sector").

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https://bugs.launchpad.net/bugs/912259

Title:
  Win32 Disk Imager Creates an .IMG file that is too big to restore to
  identical media

Status in Image Writer for Windows:
  New

Bug description:
  I used a SanDisk 4GB microSD card to create an Android (CyanogenMod
  7.1) external boot card for a Nook Color. For backup purposes, I used
  Win32 Disk Imager (either v.3 or v.4, installed on a Windows Vista SP2
  computer) to capture the image to a file, as the program permits. As
  a test, I then tried to restore that image, using Win32 Disk Imager,
  to another identical, new SanDisk 4GB microSD card. I get an error
  message telling me that there's not enough space on the new card. I
  then used a partition manager to unallocate some space on the source
  microSD card, figuring this would reduce the captured image size. I
  recaptured the image and tried again - same results. Windows reports
  that the captured image file size was not reduced on the second
  attempt, despite unallocating some space on the source microSD card.
  I then formatted the target microSD card using SDFormatter, and
  repeated the experiment; same results. Windows reports the captured
  image file as 3.79 GB in size; Windows also reports the size of a
  freshly-formatted 4GB microSD card as 3.68 GB. Obviously, the
  captured image is too large to fit on the target microSD card, but I
  am at a loss to determine why Win32 Disk Imager captures an image that
  then cannot be restored onto an identical microSD card, especially if
  there is unallocated space on the source microSD card!

  I looked at the partitions of the source microSD card after going
  through the process of installing CyanogenMod to it. The image
  installer for this process, which must be done on the Nook Color,
  creates a mixed microSD card structure that contains the following:

  Partition Type Size
  1 FAT32 415.71 MB
  2 EXT4 462.81 MB
  3 EXT4 964.84 MB
  4 FAT32 all remaining space

  Reported Total Size: 3.79 GB

  So, I can see where the image size of the image that Win32 Disk Imager
  creates comes from, but the target (blank) microSD card needs to be
  formatted to get a drive letter for use with your program, and the
  maximum size that I can seem to get with any microSD card formatting
  program that I'm aware of (including Windows) is 3.68 GB! While
  common sense tells me that I should be able to restore an image to an
  identical microSD card for backup and restore purposes, it appears
  that your program does not permit that, either due to error or by
  design.

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