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Old 10-21-2005, 06:59 PM
Winston Winston is offline
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Join Date: Oct 2005
Posts: 9
Originally Posted by dnanian
Winston -- v2.0 allows sparse images to be created, but it's not released yet. v1.5.5 only allows DMGs.

The whole thing is that a sparse image is just that: sparse. We can guess high when we create it, because only takes as much space as the data that's eventually copied to it. Guessing high when actually "testing" for size would mean we'd reject legitimate creation.

I don't quite follow you. I don't understand about the "guessing high" on a sparse image vs. "when actually "testing" for size".

Let's say you are doing a complete backup of a drive. If you know the space used on the original drive, then don't you know pretty closely how much space the sparse image will take?

SD! does not have to reject creating a backup. It could give a warning to the user that a backup might fail to happen if there is not enough space. I have had a failure to back up happen about 5 times using SD! (in part because I did not know about the need for extra space).

I have several backup drives, each with varying amounts of other data backed up on them. This is why I like using disk images - they keep the backups neat and separate. They also leave me with varying amounts of free space.

I am glad you will add a direct way to back up to a sparse image. Needing to have double the space to make a disk image backup is a big limit on my ability to back up to the drives I have.

How close is the tolerance from the original to the DMG? The disk image backup I stopped two days ago had 7GB on the sparse image, and was at something around 5GB on the DMG image - at highest compression. I understand that it may be hard to estimate the exact size of the DMG. What is the range? Is it from 90% to 100% of the original, or 30% to 100%?

It seems like SD!'s main focus is on recovering from corruption on the original drive, rather than mechanical failure.

The only major problems I have had with a drive have been mechanical failures. A running backup to a sparse image strikes me as a far better backup than having fixed backup to a DMG image. Ditto vs. the "Safety Clone" backup.

Would a Safety Clone have helped with the two catastrophic drive failures I have had? These are the only situations where I lost a significant amount of stuff (and really lost it - drive recovery specialists could not get anything off of the drive).


- Winston
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