What is the precise 4 Gig limit?

[Franko]

I may have mentioned that my main computer (A3000 with two 4.3 Gig Quantum hard drives with PFS2) got sick in 2010.  Basically, the partitions on the primary HD began to corrupt.  Then, the partitions on the backup drive also began to corrupt within a month of the first.  It is too strange that both drives would fail at the same time.  Some partitions would report that some of their data was outside their boundaries. Strange!  This has been a bit depressing for the last 9 months!

Today, I found another 4.3 Gig HD in the basement and it seems to be functional (What luck!).  While partitioning it, I wondered what would happen if I formatted all of the available 4.3 Gigs.  Would the system immediately report the drive unusable because it requires more than the available addressing range?  Or, would my system happily chug along for years until I wrote a file that went beyond the theoretical address limit?  Would that data overflow into another partition, corrupting both?

That's it for tonight's brain storm.  I may be able to finally salvage my data to the new drive.  Maybe a fresh repartitioning (inside the TRUE 4 Gig limit) of the other two supposedly bad drives will save them as well.

Any thoughts?

Using something like the FastATA MKIII hardware or the 4xEIDE hardware they spilt your drives automatically into lots of 4GB partions, but upon actually checking them they are always just a few K under 4GB (never 4GB exactly).

Seems when you try to do this due to the actual way the filesystems work if they were to actually try and write data all the way up to the very last byte of an exact 4GB partition some of the data ends up being written to the previous partition if there is one or if not it overwrites another part of the current partition causing all sorts of data loss...

The applies to the max size of a FFS partition which is supposed to be 2GB but is always just a few K less than 2GB to prevent this overwriting and corruption of other partitions...

That's the simplest explanation I can give you cos it's really a bit more complicated that this...

[Franko]

What you say rings a bell with me.  If I understand correctly, there was a natural 4 GB limit to total hard drive size (regardless of partitions) until OS3.5 or 3.9 released a patch (I didn't install these) to allow larger drives.  4 GB was a lot of HD when 3.5 was released, grin.



It only occurred to me tonight that data written past the address limit might cycle through zero to an address in my first partition.

I feel like a boob.  If this turns out to be true (I haven't yet confirmed my partition sizes), the solution will be easy enough.

It's late here.  It must be very early morning in Scotland.  You do sleep, right?  

Not very much it's only 4:10 am here and I'm still wide awake... :lol:

As I said, most folk would reasonably expect 4GB to mean exactly 4GB but in AmigaLand it's not as simple as that, even if you managed to partition an HD to exactly 4GB the file system when your HD is just about full would end up writing data to a lower partition or as you say cycle though to zero...

[Franko]

I'm still looking around for a number.  One site suggested the limit might be in the 3.7 to 3.9 GB range, depending on filesystem used.  

Appearently, Thomas wrote a utility to check the limit.  Maybe that's my answer.  I need to read up more on PFS.

I'm going to turn in tonight.  

Thanks for the help.

The number doesn't have to be exact, just make sure it's slightly under the exact 4GB size...

(gawd... I'm still wide awake and it's now 7:01am...