Sparsebundle size?

Discussion in 'macOS' started by dtemp, Jul 8, 2012.

  1. dtemp macrumors member

    Joined:
    Feb 19, 2008
    #1
    One of the best reasons to use sparse bundles is because they can grow and shrink in size without taking up more space on the disk than the data they currently contain.

    I'm curious why, when making a new blank sparse bundle disk image in Disk Utility, there is the "Size" field? I made one with the size set to 100MB and, sure enough, trying to copy a 1GB file into it failed.

    OK, so is there any drawback to setting the size huge, future-proofing yourself? Can I just set the size to 10TB and forget about it? Is there a way to edit the size of an existing sparsebundle file so it can grow past what it's initial size was set to?
     
  2. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #2
    Like you discovered, this setting is just the max size the image can grow to. So if you make a 10GB image and put 250MB of files in it, the image will only by 250MB is size. I always make the image about twice what I ever think I will need.

    You can resize an existing image by starting Disk Utility and in the Image menu selection pick Resize. That will show you the current settings and allow you to change them.
     
  3. dtemp thread starter macrumors member

    Joined:
    Feb 19, 2008
    #3
    Thanks. So are there downsides to making the size huge, like 10TB?
     
  4. Macman45 macrumors demi-god

    Macman45

    Joined:
    Jul 29, 2011
    Location:
    Somewhere Back In The Long Ago
    #4
    It's a trade off....I have a 3TB Time Capsule....I just let it run...it backs up 3 Macs. TM kicks out the oldest backups and replaces them with new ones when whatever disk you are using becomes full, I keep an eye on things, but it's pretty much a fire and forget thing.
     
  5. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #5
    Not really... the actual bundle size will only be the sun of its contents. I think there are some file system limitations with TB size like you mentioned.
     
  6. ViennaAustria macrumors newbie

    Joined:
    Jun 21, 2012
    #6
    As I discovered, there's a strange size limit to sparsebundle files. I'm not able to enlarge it beyond 16TiB (17,59TB). All tools explicitely report, that I would exceed `the´ limit. :eek:

    That's a pitty, because the server that is being backed up has already more than that size (21TB) and the TM backup server has even more (25TB). How can I use that space?
     
  7. chown33 macrumors 604

    Joined:
    Aug 9, 2009
    #7
    The 16 TB limit is a consequence of the 4KB block-size of the volume created on the sparsebundle. You can't expand the sparsebundle beyond 16 TB if it has 4KB blocks. By default, that's the block size, so you're stuck.

    In order to exceed 16 TB, you'd have to create a sparsebundle with an upper limit larger than 16 TB. When you do that, the system should calculate a suitable block size, and you should be able to grow the sparsebundle.

    Be aware that every block size will have a corresponding upper limit beyond which the volume can't grow. So choose your upper limit wisely, by considering how big it needs to be to hold what you intend to write to it.

    If you know how binary numbers work, you can calculate:
    4096 * 65536 * 65536 = 16 TB.
    All the numbers above have fairly obvious representations for those familiar with binary.
     
  8. johninsf macrumors newbie

    Joined:
    Feb 21, 2008
    Location:
    San Francisco, CA, USA
    #8
    Doing this from memory over a decade old, I think the size of the disk image WHEN EMPTY is bigger if you choose a larger maximum size. I think this is because it has to create a large disk catalog or block map or whatever. I could be wrong about this.

    But assuming I'm right, that's why you pick a maximum size for your image that gives you room to grow, but without being ludicrously over-large.
     

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