Copy of disk image still bootable?

[DavidCB]

After I have used SD 2.5 to create a bootable disk image of a drive, if I drag-copy that disk image to another drive, will it still be bootable?

Thank you,

David

[chris_johnsen]

Usually a "disk image", is a ".sparseimage" (or ".dmg", or ".sparsebundle", etc.) file. Such a file (or bundle) is not directly bootable. The problem is that the boot firmware of Macs only really supports reading files from a proper disk volume (disk -> volume -> file). But involving a disk image puts an extra layer in there, and the firmware does not handle that situation (disk -> volume -> disk image file -> disk -> volume -> file).

But a disk image can properly store all the data required to recreate a volume that is actually bootable (PPC: internal/FireWire, APM partitioned, HFS+ volume; Intel: internal/FireWire/USB, GUID partitioned, HFS+ volume). Among other details, it is this extra step of "restore before boot" that makes backups to disk image less desirable.

In any case, disk images can be copied by Finder or just about anything else and still be used to recreate a bootable volume (just use SuperDuper! to copy the disk image to a suitable volume).

If by "disk image" you mean a backup made to a volume on an actual disk, then, no using Finder to copy the files from this volume to another will not result in a bootable volume. Such a copy will likely end up missing much of the metadata required for a properly functioning system.

[dnanian]

On top of what Chris says, in general terms you don't have permission or the ability to copy full images like this. Always restore with SuperDuper! or Disk Utility, as explained in the User's Guide.

[DavidCB]

Originally Posted by dnanian

On top of what Chris says, in general terms you don't have permission or the ability to copy full images like this. Always restore with SuperDuper! or Disk Utility, as explained in the User's Guide.

Sorry if my question wasn't clear--I shouldn't have said "bootable" disk image. What I meant was, if I create an encrypted disk image (.sparseimage) and use SD to clone my hard drive to that image, I understand I can use SD to restore the drive, but if I make a Finder copy of the image, will that also be restorable?

In other words, does making a Finder copy of the image retain all its original characteristics?

David

[dnanian]

The image file? Yes. The image file can be copied around without affecting its contents (assuming, of course, a successful copy).

[DavidCB]

Originally Posted by dnanian

The image file? Yes. The image file can be copied around without affecting its contents (assuming, of course, a successful copy).

Yes, the image file is what I meant. Sorry again for misstating the question.

I was fairly certain that copying the disk image would also copy the invisible files, etc., necessary to make the restored drive bootable, but I just wanted to make sure. I have only backed up to an external FireWire drive before, never to a disk image. I understand the general concept, but I am a little bit on shaky ground.

David