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Can't mount any downloaded .ISO file with File Explorer unless I manually remove the sparse attribute from the file


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I have utorrent 3.4.3 build 40298 in windows 8.1 x64 .

In all recent utorrent versions, whenever I try to mount any downloaded .ISO file

I get "Sorry, there was a problem mounting the file" with File Explorer.

When I encountered this I thought that either the download was corrupted, or the .ISO filetype association was broken... But both were 100% ok.


Anyway, the solution is to manually remove the sparse attribute, by using this command:

fsutil sparse setflag PATH_TO_ISO 0

I know that it's caused by this advanced utorrent setting, which is enabled by default:

diskio.sparse_files: Enabling this option causes µTorrent to allocate only the data that it writes, but will inform the filesystem of the file's size (so that it can attempt to reserve enough contiguous space on the hard drive without having to physically zero all of the space out for the file). Even though space is reserved for the file, no space will be taken for the unwritten parts of the file. Enabling this option may potentially lead to increased disk fragmentation in rare cases where the drive does not have enough free space available to honor the space reservation for sparse files. Here are some things to take note of when using this option:
- Sparse files work only on partitions that are formatted as NTFS.
- Hash checking sparse files tends to be quicker than hash checking pre-allocated files, as µTorrent won't have to hash zeroed-out pre-allocated data.
- On Windows Vista, sparse files can cause µTorrent to run into a file system limitation.
- If you are using a non-administrator account with a disk quota, sparse files won't work, and the file will still get fully allocated. This is a limitation with Windows that µTorrent can't do anything about.
- This option cannot be used in conjunction with pre-allocate all files. If both options are enabled simultaneously, pre-allocation will take precedence.
- When used in conjunction with bt.compact_allocation, µTorrent will reserve space for each file in the filesystem, but it will continue to use compact writes.



Yes, the sparse flag is very useful during the downloading procedure, but the downloaded .ISO files cannot be mounted.

So, my suggestion is this:

after a torrent containing an .ISO file is completely downloaded,

utorrent to automatically remove the sparse attribute from the .ISO file.


Also, as a side note, I've noticed that, after removing the sparse attribute, the .ISO file remains binary the same, so this doesn't cause a problem with the torrent files data integrity.

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