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Reduce size of compressed disk images
Authored by: bluehz on Jun 09, '03 11:01:57AM

Did you actually compress the .dmg after noticing the larger size, or was that larger size actually after you had compressed it. Reason I ask is - OS X disk images are quite fascinating objects in that they expand and contract to suit the needs of the contents. This format fo disk image is known as "sparse" in teh documentation, and I believe that its the default when creating disk images with Disk Copy. I may be wrong - but what you might have been seeing - if you had not yet recompressed the .dmg - is possibly a temp size boost. This size difference may have disappeared when you recompressed the .dmg again. Just a theory...



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Reduce size of compressed disk images
Authored by: triplef on Jun 09, '03 11:16:26AM

I wasn't using a sparse image - AFAIK the only way to create sparse images is to use the command line tool. The larger size was after I had compressed the image with Disk Copy.



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Reduce size of compressed disk images
Authored by: rselph on Jun 09, '03 01:11:51PM

Sparse images aren't that good a solution to this problem anyway.

The problem is that the sparse image disk "driver" doesn't have any knowledge about HFS+, or whatever other filesystem is on the disk. This means that space for deleted files is never reclaimed. Once a disk sector has been touch by the file system for any use at all, it will remain part of the sparse image, even if HFS+ considers the file to be deleted.

Sparse images are really useful for building a compressed image when you're not sure of the total size you will need. But basically it's designed to be used once and thrown away.



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