Snow Leopard’s “Disk Utility” can’t create encrypted image

Two months or so I ordered the Snow Leopard DVD for my Macbook Pro. Finally I had the time to perform the upgrade from Leopard. Before actually doing so, I tried to create a disk image of my current Leopard installation. So I booted the Snow Leopard DVD and ran “Disk Utility” from it. Because the target of that disk image was an external hard drive shared by my team, I wanted to create an encrypted image.

Regardless of whether I selected “128-Bit AES” or “256-Bit AES” as an encryption method, I immediately received the following error message on screen:

Unable to create "Macintosh HD.dmg" (Cannot allocate memory)

What is this trying to tell me? No space on hard drive? Impossible, since the external hard drive is a 2 TB empty drive. Moreover, “memory” usually refers to “main memory”, or “RAM.” So is Disk Utility actually trying to read the whole 200 GB hard drive into the RAM, then encrypting it, and then creating the disk image from it?! I can’t believe that anyone would be that stupid to design a disk imaging program like this…

I finally changed the image format to “Compressed”, and presto, it worked!

Anyway, why, oh why is it so hard to generate “user friendly” error messages? And why does this happen under Mac OS X of all operating systems, supposedly being the “user friendliest” OS in the universe?

This is not the first time I receive such useless error messages in OS X. Hey Apple, care to finally make your homework???

6 thoughts on “Snow Leopard’s “Disk Utility” can’t create encrypted image”

  1. I encountered the same error while trying to backup my existing installation prior to installing Snow Leopard. The problem, I found, was the MS-DOS formatting on the USB drive and when I reformatted it with HFS+, the error went away. I suspect its memory mapping a file of the size necessary for the image, which due to file size limitations on the file system is returning and error but as its a size error on a memory mapping its interpreted as a memory error not a file size error. Hooray FAT32.

    1. I bought a 2TB Buffalo external hard drive at Fry’s for $80 (Dec 2012) and encountered this error on my first attempt to create a disk image of my Mac using the external drive as configured out of the box. The wonderful solution was using the Mac boot disk utility to first partition the external drive into two partitions and second to format one partition for “Mac OS Extended” and the other for “FAT32” which only took about a minute to accomplish. Then I backed up my Mac to one partition and my PC to the other. Thanks to this blog for the useful information.

  2. @James: I’m not sure whether what you write is actually true.

    Remember that I just changed the image type (from encrypted to compressed), and that made it work!

    In both cases, the final size of the image was not known in advance (because you can’t predict the “output” size of encrypted or compressed data, usually compression occurs before encryption is applied).

    Mind you, I did not change the filesystem of the target drive!

    1. Administrator. James is right. I just did it and works. The drive where you are going to record the image has to be formatted with mac system. HFS.

      The disk has to have enough space. Check it.
      Has to be formatted for MAC System.
      I Disk Utility you click Erase> click The HDD the you want to format. Choose the system. End click erase.

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