What is a Sparse Disk?

Question

What is a Sparse Disk?

I am struggling to get a backup onto an external Ethernet Hard Drive I have attached to my network. I am told by tech support for the back-up software (SilverKeeper) that the problem may lie in the fact that I am trying to use a "sparse disk image" on the network drive.

The drive is currently formatted in FAT32 because I have 2 Macs and 1 PC using the drive. The suggestion is to reformat it using HFS+ or EXT3 but if I use HFS+ I don't think the PC will be able to write to or read from the drive. I can't partiction the drive because I want all three machines to share a common music library for iTunes.

Can someone tell me what a "sparse drive image" is? Will reformatting the drive to HFS+ eliminate the problem (assuming I can overcome the PC issue?

Thanks,

David

Posted on Sep 27, 2005 1:47 PM

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Answer 1

AJ

Level 5

7,075 points

Sep 27, 2005 2:41 PM in response to David Schwartzer

From what I gather, a sparse image is one where the size of the image can dynamically change. that is, when you create a dmg with Disk Utility, you have the option to create an image of specific size - for illustration, say 4.7gb. When you create the image, it consumes 4.7gb regardless of the actual amount of data you put in the image.

(If you try to put more than 4.7gb of data in illustration dmg file, it wont let you.)

A sparse image does not have a preset size limit. As you add to it, it grows dynamically to the size of the sum whatever the actual file sizes happen to be.

to do this, it may leave out some sector information, whihc may cause non-apple standard formatted disks to not be able to properly read/write the file.

You are correct - reformatting the drive as HFS+ will render it unreadable by a windows box.

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Answer 2

Nov 2, 2005 3:56 PM in response to David Schwartzer

I have similar experience using Sparse Disk image on a non HFS formatted drive: FAT32 or unix format seems not compatible with Sparse Disk image file.

After creating an encrypted Sparse Disk image on a FAT32 external drive (connected with FW800) I did not manage to eject (i. e. unmount, even after logout) the disk image after copying 4Gb of Data, after reboot, the image was corrupted.

After reformating the same external drive to UNIX, some files failed to be copied (error code -36) in a the Sparse Disk image.

So I reformated the drive with HFS and every thing works fine.

To be able to use the drive with Linux, I would use HFS+ Linux driver ( http://www.ardistech.com/hfsplus/ : Alpha dev), for windows, I would use MacDrive ( http://www.softpedia.com/get/File-managers/MacDrive.shtml : delivered with my drive, so it should work)

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