Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am trying to do a full backup of a drive on a Mac I have. The drive has 96GB of 100GB filled up. I have an external USB drive I want to backup to. On the external drive, no one file can be any larger than ~4GB.

How do I create or find an already segmented and empty dmg that I can put on the external USB?

I know that I should be able to create a dmg and then segment, but with the available resources, it will have to be in one step. Curious how I might get to this point. I figured there must be some zipped up, large, segmented dmg parts somewhere that someone has already created... kind of like those large empty floppy images from back in the day.

Thanks, Chenz

Update: This is the command that allowed me to create the sparsebundle with AES encryption...

hdiutil create -megabytes 200000 -layout SPUD -fs "Journaled HFS+" \
-type SPARSEBUNDLE -encryption AES-128 -imagekey -stdinpass \
/Volumes/My\ Passport/Backup-Before-Fan-Replacement/bundl.sparsebundle
share|improve this question
up vote 2 down vote accepted

How about using a sparse bundle disk image? They store their contents as a series of "band" files (default size 8MB, but you can change this if you create them at the command line with hdiutil with -imagekey sparse-band-size=size), giving the effect of an image that segments itself as it's created.

share|improve this answer
+1 for sparsebundles. – Chealion Jun 10 '09 at 14:52
sparse-band-size is not a size in bytes, it is a number of sectors (a sector is 512 byte, so putting 8 there means 8 * 512 = 4096 bytes). And it is also not the size of a band file, it is the number of sectors by that a sparse image grows each time it has to grow; and this applies to sparse bundles just like to sparse images (that are not bundles). – Mecki Jul 12 '10 at 10:32

Stuffit Link apparently will span multiple drives - so I presume it will split the the archive into 4GB chunks.

As an aside is it not possible to create a partition on the external drive not using FAT32, to remove the 4GB limit?

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.