Large (15tb) sparse disk image taking a LONG time to create-- is there a size limit?

Discussion in 'OS X Mavericks (10.9)' started by Obioban, Oct 7, 2014.

  1. Obioban, Oct 7, 2014
    Last edited: Oct 7, 2014

    Obioban macrumors regular

    Oct 19, 2011
    I have a drobo with 16tb available. I'd like to make a sparse disk image on it so I can encrypt everything on the drive.

    When I make one in disk utility, it takes a LONG time-- as in, it's been going at it for two days now. The file it's creating also seems to be growing (where as sparse image files are only supposed to be as large as the files they contain, and grow to match).

    Is there an upper limit on sparse image size, and this is never going to complete? Or, something else going on here I'm not understanding?

  2. Obioban thread starter macrumors regular

    Oct 19, 2011
  3. Satori macrumors 6502a


    Jun 22, 2006
    With a 4KB block size (the default), 16 TB is the maximum. Therefore I don't think you're up against a maximum here.

    Are there any files already on the Drobo? I'm not sure whether this would affect the maximum sparse disk image you can create (even if the actual image size is only as big as the files that it contains).

    Perhaps you could experiment with trying to create a slightly smaller image (e.g. 12TB) and see what happens.
  4. NoBoMac macrumors 68020


    Jul 1, 2014
    Has this worked in the past? With, say, a smaller sparse image?

    There was a thread a month or so ago, and that person could not get it to work. Issue could have been that the file server drive/partition needed to be OS X format, and server supports AFP.

    The following is for Time Machine, but since that's a sparse bundle as well, might be germane:

    As Satori said, try a smaller image first. I'd say make a few GB image and try copying a couple of files back and forth first, to see if it's possible to begin with, before ratcheting up the image size.
  5. mfram macrumors 65816

    Jan 23, 2010
    San Diego, CA USA
    I'm guessing the O.P. is connecting to the server via SMB. And SMB may not support sparse file operations on the Mac. Maybe try connecting over AFP or NFS.
  6. Obioban thread starter macrumors regular

    Oct 19, 2011
    Local disk, not connected over the network. I just tested with a 10gb disk image and it created instantly.
  7. Obioban thread starter macrumors regular

    Oct 19, 2011
    Been playing a bit more...
    10gb unencrypted, creates in ~4 seconds, 49 mb image file.
    10gb 256bit encryped, creates in ~4 seconds, 49 mb image file

    Saw above that 16tb is the limit of size, so I thought maybe I was playing it too close to the sun, tried a 14tb image. Currently it's ~1 hour in and still going, disk image file is sitting at 400mb and increasing...

  8. Obioban thread starter macrumors regular

    Oct 19, 2011
    14tb image completed overnight. Final blank image size is 1.97 gb-- bigger than I expected by a long shot, but certainly not a problem.

    Looks like I was hitting the 16tb cap making a 16tb image! I left that trying to create for over a week without success.

    Starting a 15.75tb image now to see how close to the limit I can get it.

    Thanks for the help!
  9. YanniDepp macrumors 6502


    Dec 10, 2008
    I'm not surprised it takes so long to create a 15 terabyte disk image. I genuinely don't want to know why you need to do that.

    Disk file systems have an index of which files live where. Depending on the format you're using (FAT, NTFS, HFS), it'll be the file allocation table, or superblocks, or something equally boring.

    Even if your disk is totally empty, it'll still need to create those data structures as it's being formatted. It needs to create a record of all the "blocks of data" on the virtual disk, and the fact that they're empty. That's why your empty disk image is using a few gigabytes. It's pretty much a record of "here's 15 terabytes worth of small chunks of disk where nothing lives".
  10. NoBoMac macrumors 68020


    Jul 1, 2014

    And seeing a different thread on here re: FileVault, reminded me it would have been easier and just as effective to reformat the drive to "journaled" and enable disk encryption with a Keychain Access randomly generated key (25+ char) and let Keychain remember the key (no need to rekey in when plugged in).

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