There are various further restrictions due to hardware architecture:
- A1200/4000/600 IDE is limited to 2 GB (32 bit block address)
- many SCSI controller (e.g. WD33C93 based ones) are limited to 2 GB (32 bit block address)
Some of these can be worked around.
This should read 2 TB in both cases.
I'm probably more than a little confused. 
I beleive there was a problem (before OS3.5 and also PFS2) addressing drives larger than 4GB. I'm beginning to beleive this was a limitation of FFS. I don't know if the limits were the same for SCSI and IDE.
It doesn't seem now that this was my original problem. I'm left at the moment with several possible causes: PFS2 has a bug, my poor understanding and setting of drive parameters (mask, maxtranfer, etc), too many small files (like those generated by iBrowse, Yam, Palm synchronization, etc) that are constantly being revised, drives do have a finite lifespan.
The problem is in the interface between file system and device driver. It is not specific to 3.1 and below and it is not magically fixed in 3.5 and above. You need to find a combination of file system and device driver which works together in order to bypass the 4GB limit.
The other problem is that the so-called standard was made without talking to the other parties which already had developed a fix. Therefore now there are two "standards" which can be used to bypass the limit, but they are not compatible.
The standard which came with 3.5 is called NSD.
The other command set invented by a group of third-party hardware manufacturers in the time before 3.5 came out is called TD64.
There is a third possibility called Direct-SCSI a.k.a. HD_SCSICMD which has some other limits.
Now fact is that PFS2/3 support TD64 but not NSD, so they do not work with OS 3.5's device driver for the internal IDE controllers on Amiga motherboards. For large hard drives, that is. Hard drives smaller than 4 GB can be accessed by every file system.
