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A possible fix for 'overlapped extent allocation' errors
Authored by: johnsawyercjs on Dec 11, '03 03:02:25AM

And here's my hard drive directory damage story...

I think it's possible that booting back into OS 9, with large (greater than approximately 25 gigabyte) volumes containing hundreds of thousands of files, even when they're HFS Plus/Mac OS Extended volumes, may sometimes damage the directory on those volumes, since OS 9 may be less "robust" at handling large volumes with lots of files; that, plus excess fragmentation may have played a part, as described in some posts above. About a year or so ago, when I was using drives smaller than 40 gig on a beige desktop G3, exclusively under OS 9, I had occasional directory damage, but nothing like the frequency I began to see when I started using 40 gig and larger drives, initialized as a single volume. When I started using 40 gig and larger drives, again under OS 9, I began to see directory damage occur more frequently, several times over the past year. After my 40 gig crashed bad, and wouldn't appear on the desktop, I recovered its files onto a 60 gig, leaving about 20 gig of free space for a while. It ran fine under OS 9 for several months, then as I began to fill it up, it crashed too, with significant directory damage, causing it to appear on the desktop only occasionally, so I recovered its files onto an 80 gig drive, partitioned as a single volume, which I used under OS 9 for about a month, after which I replaced the beige G3 with a Blue&White G3 so I could run Panther. After I installed Panther onto the 80 gig, I was in the habit of booting back and forth between OS X and OS 9, depending on what I needed to do. Within a few weeks, the 80 gig's directory was damaged and needed recovery. I began to wonder if the increasing volume size might be one factor, and wondered what would happen if I partitioned my drive into smaller volumes. I hadn't seen the directories on my earlier, smaller drives (10 and 20 gig) get damaged so quickly, running under OS 9, so I decided to see how 25 gig volumes would fare. I used Disk Utility from OS 10.3 to initialize my 80 gig drive into three equally-sized 24 gig volumes, then I copied my files to them, leaving at least 8 gig free on each, and now I've booted into 9 several times since, and have checked the directories on the 24 gig volumes several times, and none of them has had any directory damage after booting into OS 9 and then back into OS X. So the lesson may be: If you use volumes larger than about 25 gig, don't boot back into OS 9 if you can avoid it, and if you do, stay in OS 9 for as short a time as possible; if this isn't practical, partition your drives into volumes no larger than 25 gig. I know a lot of people will find that they've gotten along fine with volumes larger than 25 gig, even though they boot back into OS 9 frequently, but that's the old YMMV (Your Mileage May Vary) phenomenon.



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