Single-user mode: How to mount and access an external USB drive?

Question

My MacBook Pro HD is acting up. Cannot boot normally or into "safe mode". Cannot reinstall OS without wiping out the HD. Need to recover some critical files but DiskUtil First Aid and Restore options cannot successfully complete. Problem traced down to "invalid node structure" which means I either have a hardware problem or my filesystem partition directory structure is corrupted. I need to recover some files that are not backed up (timin issue with my regular backup process).
I can boot into single-user mode, mount the root file system (/sbin/mount -uw /) and can see/navigate the rot filesystem structure via good UNIX command line. Here's what I would like to do (in single-user mode):
1. Mount an external USB drive (250 GB already formatted as Mac OS X Extended)
2. Copy various files and/or directories from my HD to the external USB drive (UNIX cp command)
I realize I could go spend $$ for the Disk Warrior or Data Rescue products (or something similar) that SHOULD help me recover my HD or files, but it seems silly to do this when I can see, touch and taste them from within single-user mode....
Comments? Suggestions?
TIA --
Trent
P.S. Once I've recovered my files, I'll try to reformat the HD and then reinstall the OS. And THEN go have Apple look at my machine (thank goodness for AppleCare coverage)!

Answer 1

Resolution:
1) Boot system in single-user mode (SUM) with external HD attached.
2) Execute the following UNIX CLI commands once SUM boot process is completed:
# fsck -fy
# mount -uw /
# mkdir /Volumes/target_directory
# mount -t hfs -w /dev/diskXXX /Volumes/target_directory
# cp -RXv /source_directory /Volumes/target_directory
Where XXX is the device-level name for your external HD's data partition. In my case this was /dev/disk1s2. It may take some experimentation to identify this device name if your system has multiple HD's.
3) Verify contents were successfully copied onto the /Volumes/target_directory.
Comments and observations:
- Do NOT use "/" as your source directory - cp will make a second (redundant) copy of /volumes/target_directory
- I was able to successfully copy ALL files off my HD despite the fsck command's "invalid node structure" error message with this simple procedure. YMMV, depending on the state of your HD.
- The repeated disk0s2: I/O error warnings displayed during the SUM boot process did not seem to have a negative effect on this procedure. I also received this same error warning intermittently as I navigated the mounted filesystem did not seem to be a problem, either. Again, YMMV.
Commercial software:
I downloaded ProSoft Engineering's Data Rescue 3 product (trial version) before spending $99 to attempt to recover my "bad" HD's data via mounting to a good system with FW target mode. It could not successfully complete its "QuickScan" process and immediately hung on block 0 of 390M during its "Deep Scan" process. The product did seem to function properly on an operational system. ProSoft's technical support was responsive and helpful but had no answer for my "Deep Scan" error.
I did not attempt to use Alsoft's Disk Warrior 4 product. I could not find any trial software available and was reluctant to spend $100 based upon the mixed reviews and comments on this discussion forum as well as other reviews. Alsoft does claim to address the "invalid node structure" error in their marketing materials. Hindsight being 20/20 - I saved $100 by using this simple procedure.
Final note:
Neither Leopard nor Snow Leopard's installation DVD could recognize the bad internal HD when trying to do a reinstall. While DiskUtil was able to "see" the bad internal drive it immediately failed when I tried to do an "erase and format". Took the system to my local Apple store and the Genius ran a tool called "SMART Utility" from Volitans Software (www.volitans-software.com). SMART utility confirmed that my HD was bad so it was replaced. AppleCare pays for itself (once again!).