"Invalid node structure" on a supposedly failing HDD. Looking for tips and suggestion


macrumors 65816
Original poster
May 21, 2006
I have a mid-2007 iMac (specs in sig), so the computer is about ~5 years old. It's treated me great for many years, but about six months ago, I ran into some problems. Flash videos were pretty darn laggy and would lock-up my whole computer for a couple seconds at a time; applications were taking longer to open, the system as a whole felt sluggish, and boots were taking 2-3 minutes versus ~30 seconds like they should.

I went to repair permissions, and there were hundreds of permissions problems. I then went to repair the disk, and it told me that the operation couldn't be continued due to an "invalid node structure." So, I decided to completely wipe the drive and do a fresh install. That seemed to Band-Aid the problem. It still didn't feel near as snappy as it should; but the computer was at least usable.

Tonight though, a storm knocked out our power. Upon re-booting my iMac, the boot took a good 7+ minutes :-/ Once again, everything is sloooooow. And again, all my permissions were f-ed, and it seems I once again have an "invalid node structure."


So, my questions:

1) What exactly *IS* an invalid node structure?

2) Is it safe to assume this HDD is pretty much ****ed? Or might there be something else I'm missing?

3) And lastly - and this is more subjective - what do you guys think of putting a ~120GB SSD in the iMac, instead? I don't have much disposable cash. But, I need this computer to work so I'm gonna have to fix it. And I'm looking at my free space; and on my current drive, after 4+ years, I've only used ~80gigs. All my media and stuff is on my PC, and all my Adobe projects are on an external. Plus I have lots of space on my NAS. Considering a 120GB SSD is about the same price as a 500GB HDD right now, I'm kind of thinking of just going with the smaller, but much faster, storage. Am I crazy?


macrumors regular
Mar 5, 2011
You really should take a look at this thread hereand search for similar threads on this forum or the net.

The bottom line is that it is probably your hard drive failing. If you are really unlucky then it could even be worse. The conundrum is that to find out if it IS worse, it's going to cost you even more cash just to have it diagnosed. Now you could purchase the SSD and if it is the main board thats going/gone the problem will still be evident. At that point you could still however use the new SSD in any new Mac that you might purchase, so buying the SSD isn't necessarily a bad thing to do.

My own point of view is that your machine has given 5 years of service and these things do tend to have a finite life. You could patch it up only to find that in 6 months another problem makes it un-economical to repair. Or you could find that the new drive is all that is needed and the machine easily lasts another 5 years.

I would simply replace the failing drive with a non-SSD drive and start saving for a newer model Mac. The cost of even a 120 GB SSD is still a fair percentage of the cost of a new/refurb 21.5 inch current base spec iMac. Apart from the screen size (assuming you have a white 24 inch iMac) a current non-SSD base spec iMac will give you a much better overall experience than simply placing a new SSD in your 5 year old machine. Putting new money into an old PC is always risky. Minimise that risk by putting as little cash into it as possible buy buying a standard drive, not an SSD.
Last edited:


macrumors 6502a
Oct 20, 2009
It might be time to retire that machine, but give diskwarrior a try.

"The Invalid Node Structure means that the cataloging system that keeps track of where everything is on your hard drive is b0rked. TechTool Pro may fix it, as may DiskWarrior -- however some people have reported no success with both. If you haven't already make sure your data is backed up! Do it now! Ultimately, a reformat of the hard drive is the last solution." That's what was posted by another MR user.

It might not entirely be a mechanical issue.


macrumors 601
Jul 17, 2010
Ultimately, a reformat of the hard drive is the last solution." That's what was posted by another MR user.
I don't know... Backing up a .dmg image and reformatting and cloning takes very little time. If the disk is malfunctioning Diskwarrior will most likely let you know.
I'd run DW 1st. Replace the directory if I can and backup to a .dmg of choice. That way you have a very nicely de-fragged volume to image whatever you need with. Either reformat and test out the same drive after applying the image or just buy a new HDD because my data is worth much more than 200.00.
I am with you though if you reformat and have no backup and just build from scratch app by app etc. it would be a last frustrating resort.


macrumors 6502a
Oct 20, 2009
It's most likely just directory issues, but given the age of your machine, hardware failures can't be ruled out.


macrumors 68000
Sep 10, 2008
Asheville, NC
The fact that it's so slow points very heavily to the hard drive, and this is an issue that none of the Mac-specific hard drive tester programs will tell you about. Disk Warrior will only tell you if it comes across bad blocks in the directory structure, which at this point sounds pretty likely. Yes, it's a bad directory structure, but it's almost certainly caused by a bad hard drive, which is evidenced by how much the machine has slowed down.