View Full Version : Sparse image: And the point would be, what?

08-08-2009, 01:04 PM
Admittedly I may be misunderstanding, but could somebody please disabuse me of the notion that a "Sparse Image" is usless.

Follow me:

I want to back up a 500g external portable disk onto a 1gb internal. So I create a sparse disk image on the 1gb Internal - IMPORTANT NOTE this is NOT my startup disk. I initiate the back up.

PROBLEM: while there is more than enough space on the 1GB internal disk, it would seem that even though the data is being written to this disk, the sparse image actually mounts to the startup disk. Hunhhhhh???? yes. It appeared that the disk image was actually taking up disk space on my startup drive as well as a kind of mounted volume. Does this make any sense at all???


08-08-2009, 01:14 PM
No, that doesn't make any sense. Are you certain that's what was going on? Why do you think it was taking up internal space?

08-08-2009, 01:20 PM
So to be clear... When you "mount" the sparse image it does not have to allocate disk space on your startup disk?

Honestly that's what seems to be happening. If I watch the image on the 1gb internal (non-startup disk) as the data is being copied, it is growing like a disk being written to. However my startup disk is also shrinking at the same rate. Even though I can clearly see that the sparse image resides on the NON-STARTUP disk.


08-08-2009, 04:34 PM
No, mounting a sparse image does not allocate disk space on the startup disk, unless it -- for some reason -- causes your swapfile to increase, or you're running some other program that's taking space.

Are you running AntiVirus software, or anything similar?

08-08-2009, 06:16 PM
I'm trying to do a network backup to an Airport drive (a LaCie USB drive hooked up to a new Airport Extreme).

Following the directions (I think), I did an initial backup to a sparse image with the LaCie drive connected directly to my MacBook Pro. No problem.

Then I reconnected the drive to the Airport, verified that it was mounted, and set up a Smart Update to the image. After several "failed to mount" error messages, the update eventually got underway and ultimately failed with an "out of disk space" error. Moreover, I now discovered that the internal drive of my laptop was full and, after a little detective work, realized that the new image was created on the internal drive rather than the networked drive.

I've repeated this whole sequence twice more with the same outcome.

What am I doing wrong? Why is SD putting the smart update on the local drive?

08-08-2009, 06:20 PM
I don't quite know what you're doing wrong. It sounds like, perhaps, you didn't mount the Airport Disk first, and tried to navigate to it through "Network"? Or, perhaps, the connection to the drive failed, and thus the mount point got created in /Volumes?

Where, exactly, was the new image created?

08-08-2009, 06:24 PM
Yes to /Volumes. That's where it was.

But I'm pretty sure the Airport drive was properly mounted.

(Thanks for the prompt reply, by the way. It's an awfully lovely day in Weston to be hanging by the computer!)

08-09-2009, 09:45 AM
If it was in /Volumes, that generally does mean the destination failed mid-copy, so the mount point converted to a folder during an internal retry. Your network connection has to be reliable for network backups to work well.