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Small disk images may not have much usable space System
When you use Disk Utility to create a new disk image, it defaults (at least in 10.5) to setting the Volume Format to 'Mac OS Extended (Journaled).' Normally, this isn't an issue, and it's the best setting to use. However, if you're creating a small disk image -- perhaps a 10MB encrypted image to hold your financial records -- it can be a problem. That's because the journaling information takes up about 8MB on the disk image. Add in the space lost when formatting, and you wind up with only 1.7MB of usable space.

So if you really need at least 10MB of usable space, create a 20MB disk image instead. Alternatively, you can change the Volume Format to 'Mac OS Extended,' and this will disable journaling on that image. Of the two choices, I've chosen to go with larger images with journaling enabled for those times I need a smaller disk image.
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Small disk images may not have much usable space | 4 comments | Create New Account
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Small disk images may not have much usable space
Authored by: Clint MacDonald on Jan 17, '08 09:18:16AM
So if you really need at least 10MB of usable space, create a 20MB disk image instead.
Good tip!

Best wishes, Clint



[ Reply to This | # ]
Small disk images may not have much usable space
Authored by: TheCrunge on Jan 17, '08 09:47:29AM

Or you can create a .sparseimage that will "stretch".



[ Reply to This | # ]
Small disk images may not have much usable space
Authored by: osxpounder on Jan 17, '08 10:30:16AM

It will stretch, but it won't shrink, so if you "churn" files a lot on a sparseimage [change, remove, and add], you might want to go to Terminal now & then and "compact" that sparseimage again, to reclaim lost space. Deleting files from a sparseimage doesn't free up the space they claimed, it seems.

hdiutil compact MyFile.sparseimage"

I learned this from a tip at this site.



[ Reply to This | # ]
Small disk images may not have much usable space
Authored by: nekomatic on Jan 18, '08 02:38:12AM

Does it make sense to have journalling turned on for a disk image anyway, especially if the image file itself is stored on a journalled disk?



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