Does anyone have a really clear idea of how Disk Utility / asr creates and
restores multi-partition disk images?
In the simple case of making an image of a JHFS+/X volume, I expect I can
restore it to a partition of a different size and the volume is resized to
match the partition size. I'm pretty sure I've done this a few times. I'm a
little vague on whether these were block copy based images or file copy based
images. I don't know if it matters with the most recent version of asr, maybe
even for some time.
Not clear to me is whether a single disk image, across multiple partitions
(e.g. Mac OS + Windows using a BCA created partition) produces a mixed "file
copy" and "block copy" image? Surely asr isn't going to file copy the Windows
partition, rather it would be block copied, but then it can't do a block copy
for the live Mac OS system that's running this Disk Utility event. So? What
happens?
I know you could boot off some other disk, and then easily do a block copy of
the entire source. But then the questions I have are:
a.) Isn't the resulting image file, without compression, exactly as big as the
entire source disk? i.e. it would functionally be the same as using dd on a
block level device: you get an image file with exactly the same number of
sectors in on the source. Right?
b.) When restoring a block copy image, it doesn't seem possible to restore to a
smaller disk. Just like you can't do this with a dd based image. There's no
means for the resizing to occur until all sectors are restored. What about
going to a bigger disk? Seems like you're stuck because the typical sequence of
the restored partitions (which will be restored in their original state from
source in every way):
EFI System partition
Mac OS
Recovery HD
Windows NTFS
<Unallocated>
That unallocated space as a result of the replacement disk being larger, isn't
accessible. Since it doesn't butt up against Recovery HD, the resizevolume nor
mergepartition options in diskutil from the command line aren't going to work.
Which means there isn't a GUI option either from within Disk Utility. I can
cobble together a solution (to this hypothetical situation) using a combination
of gpt and gdisk, but it appears Disk Utility isn't really a practical solution
for backup and restore of a disk that contains multiple partitions including
Windows Boot Camp partitions.
And I'm wondering if I'm wrong because when I read the asr man page it says
something rather confuzzling:
"In addition to geometry requirements for supporting block copies, asr requires
that the
source and destination filesystems be compatible. A non-HFS+ source can
only be used
to perform a file copy."
I don't understand how asr will do a file copy from NTFS to NTFS when we don't
have read/write NTFS by default (or even officially supported if you change
this behavior). Or why asr couldn't do a block/sector copy of NTFS to a disk
image - it's just data, it doesn't have to understand it.
Alright this is long enough...
Chris Murphy
Chris Murphy
Color Remedies (TM)
New York, NY
----------------------------------------------------------------------
Co-author "Real World Color Management, 2nd Ed"
_______________________________________________
MacOSX-admin mailing list
[email protected]
http://www.omnigroup.com/mailman/listinfo/macosx-admin
