Sparse Images

ricede · 05-29-2012, 03:26 AM

i am not sure which forum to put this question in - please move if this one is not appropriate. Thanks.

I wish to make a restorable dmg of my HD using CCC. I am not sure whether to make a read write sparse image or just a read only image. I have googled it & read through the CCC site & don't seem able to find the relevant answer.

I would prefer the read write sparse image as i can continue to update it - i just want to make sure that i would be able to restore from it, through disk utility, should my internal HD go down.

acme.mail.order · 05-29-2012, 05:18 AM

From the "read / restore" end of things there is no difference between any type of disk image.

From the "write" end there is a big difference.

Read only is meant for snapshot-type archives. Their original purpose was transmitting a floppy disk to the duplicating plant over the telephone.

Read/write images will be a fixed size, no matter how much they really hold. A 10Gb image containing a single small text file will consume 10Gb.

As you have probably worked out, sparse images can grow with their contents (but they do not shrink with their contents) and are the preferred choice for archiving.

Another option is a sparse bundle - same as a sparse image but composed of many smaller files rather than one big one. Developed to be more compatible with Time Machine - only the changed parts need to be copied.

chabig · 05-29-2012, 05:30 AM

If you want to be able to update it, it must be read/write. Your only other choice, then is between a sparse image or a sparse bundle. Sparse bundles were introduced with Leopard and so are slightly newer. I'd choose that.

ricede · 05-29-2012, 05:58 AM

Thanks. I shall use a sparse bundle.

05-29-2012, 03:26 AM	#1
ricede All Star Join Date: Jul 2008 Location: India Posts: 505	Sparse Images i am not sure which forum to put this question in - please move if this one is not appropriate. Thanks. I wish to make a restorable dmg of my HD using CCC. I am not sure whether to make a read write sparse image or just a read only image. I have googled it & read through the CCC site & don't seem able to find the relevant answer. I would prefer the read write sparse image as i can continue to update it - i just want to make sure that i would be able to restore from it, through disk utility, should my internal HD go down.

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05-29-2012, 05:18 AM	#2
acme.mail.order League Commissioner Join Date: Sep 2003 Location: Tokyo Posts: 6,045	From the "read / restore" end of things there is no difference between any type of disk image. From the "write" end there is a big difference. Read only is meant for snapshot-type archives. Their original purpose was transmitting a floppy disk to the duplicating plant over the telephone. Read/write images will be a fixed size, no matter how much they really hold. A 10Gb image containing a single small text file will consume 10Gb. As you have probably worked out, sparse images can grow with their contents (but they do not shrink with their contents) and are the preferred choice for archiving. Another option is a sparse bundle - same as a sparse image but composed of many smaller files rather than one big one. Developed to be more compatible with Time Machine - only the changed parts need to be copied.

05-29-2012, 05:30 AM	#3
chabig Hall of Famer Join Date: Jan 2002 Posts: 2,930	If you want to be able to update it, it must be read/write. Your only other choice, then is between a sparse image or a sparse bundle. Sparse bundles were introduced with Leopard and so are slightly newer. I'd choose that.

05-29-2012, 05:58 AM	#4
ricede All Star Join Date: Jul 2008 Location: India Posts: 505	Thanks. I shall use a sparse bundle.