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backup mac hfs partition with dd

Subject: Thanks All for help with dd backup
From: Mark Conrad <nospam@iam.invalid>
Date: Sun, 01 Jun 2003 02:22:34 GMT

Howdy all -

Thanks for all the help with the 'Terminal' method of backing up an OSX
partition, using the command "dd".

dd works great as a backup/restore tool, providing me with a bootable
"mirror" backup of a 1.5-GB OSX operating system in a 12GB OSX
partition in 3 minutes time:

dd if=/dev/rdisk0 of=/Volumes/Disk-4/Bak bs=524288 count=3000

Now I can zap OSX to my heart's content, experimenting with 'dangerous'
shell commands, knowing that I can restore the OSX partition quickly:

dd if=/Volumes/Disk-4/Bak of=/dev/rdisk0 bs=524288 count=3000

I was having trouble getting the restored OSX partition to pass
inspection by the DiskWarrior utility, kept getting "Critical Errors in
Volume Information".

This error never occured if OSX was installed "fresh" from its CD, then
checked with DiskWarrior, very puzzling.

Finally got rid of that error, by making a seperate tiny backup of the
very last 512-byte sector in my OSX partition, the so-called "Alternate
Volume Header" sector.

I actually "bracketed-in" that sector by creating a 5-sector backup,
each one of the 5-sectors being 524288 byte sectors.  The resulting
additional tiny backup file is less than 3-MBs, and takes about
3-seconds to create:

dd if=/dev/rdisk0 of=/Volumes/Disk-2/Bak2 bs=524288 iseek=20480 count=5

After the main restore operation, which takes roughly 3 minutes to
complete, the tiny additional backup file created above is 'restored'
to the same OSX partition, taking a few seconds to pump in the tiny
file---

dd if=/Volumes/Disk-2/Bak2 of=/dev/rdisk0 bs=524288 oseek=20480 count=5

In all likelihood, messing around with the tiny file is unnecessary,
because DiskWarrior can quickly "repair" the error.    I just feel
better taking positive steps to keep the error from occuring in the
first place.

I hesitate to backup the entire 12 GB OSX partition with dd, because
that would take about 24-minutes.  I prefer to backup just the 'active'
part of the OSX partition, which in the case of the experimental
(small) OS 10.2 - - - took up less than 900-MBs space on disk.  I
allowed a safety margin, about one and a half GBs total file size,
which accounts for the monstrous 3-minutes that it takes dd to create a
backup file.

My real OS 10.2.6 is a bare minimum of 3.2-GBs in size, and by the time
I get it loaded up with the app's that I desire, that 'bare-minimum'
size will get up near 5-GBs.

That 5-GB size would take 10-minutes to back up.

The 12 GB partition should give OSX plenty of breathing-room.

Mark-

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