WildBill's Blogdom

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"Overlapped Allocation Extent" - WTF?

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Got an “overlapped allocation extent” error on my Powerbook’s filesystem (running 10.3.3) last night. Nasty - it’d completely hang DiskWarrior. I’d never thought I’d see a problem that ol’ DiskWarrior couldn’t fix.

Luckily, though, the Mac OS has a way to fix that error without any thirdparty tools, though it’s not documented. Here’s how:

1) Run Disk Utility on the affected partition and select “Repair Disk”.
2) Disk Utility will run through, and try to repair everything. At some point it’ll toss an “Overlapped Allocation Extent” error, followed by a number (in my case it was 153187d - the “d” is for “decimal”).
3) Disk Utility will complete. It’ll say that the filesystem was fixed, but if you run it again it’ll toss the OAE error again. Subsequent runs of Disk Utility (or fsck, for that matter) will behave the same - the OAE will be tossed, and then it’ll say that the volume was repaired. What*ever*!

So now note that decimal number. That’s the inode that has the cross-linked file. :) So, now we need to find the file that’s cross-linked and remove it (if we can - hopefully it’s not part of the core OS).
Running “find / -inum -print” will tell the OS to go off and find the file that’s associated with the inode specified. In my case, it came up with two - an entry for a Virtual PC diskimage file (which I really never used), and an entry in my Mozilla cache.

I deleted both files, rebooted, and fsck/Disk Utility reported the filesystem as fixed. Hope this helps someone else.