just adding this here as i had issues myself
The CHS drive size issue
Problem: If, on a system limited to CHS addressing, you access a drive that was initialized and partitioned on an LBA capable system, you will get in trouble if the last partition of the device is extended to the very end of the drive.
Applies to: Devices of any size up to 7,87GiB (including 8GB CF/SD cards), initialized in any way in WinUAE, or in OS3.5/3.9 HDToolbox on real HW, and then used somewhere else without a scsi.device patch.
Also applies to 16/32GB SD cards used without scsi.device patch on clever ide-sd adapters, and to IDE devices initialized on a SCSI-IDE adapter with OS3.5/9, and moved to IDE without scsi.device patch.
Reason: Total drive size by LBA is exact, but by CHS it is limited to multiples of Heads and Sectors-per-track.
It is common for devices to report the full size with LBA, and a slightly smaller size with CHS. Hence, with CHS you are not able to address the last blocks of the drive.
WinUAE does not retrieve the size information directly from your device, but uses what's provided by Windows, so even when using WinUAE's IDE HD-controller you get the full size.
Consequence: With FFS or regular PFS you will get read/write errors when you attempt to access the last area. (IE when the last partition is ~half full, as partitions fill up from the middle)
With SFS or PFS AiO the last partition will not mount.
(It will not destroy data, you'll simply be unable to read from or write to this area.)
Solution: Patch scsi.device, or reduce the RDB size definition by 2 MiB or more, or leave 2 MiB or more unused at the end of the drive.
Or you can initialize the drive on a real amiga with WB3.1, or with OS3.5/3.9 using HDToolbox from WB3.1 or older.
It's just the drive definitions that need to be done in the old version, the partitioning can be done in WinUAE or OS3.5/3.9 HDToolbox.
(This 'old hdtoolbox in OS3.5/3.9' scenario is not thorougly tested, but as long as HDToolbox reports maximum 16 Heads and 63 Bytes per track you're fine)
Why 2MiB? 2MiB is largest discrepancy between CHS and LBA size. For ATA compliant devices it's only 504KB (16 H x 63 SPT x 512 B), but up to 2MiB within CHS theoretically (with 256 Heads).
If you want to check if your existing drive is affected, run a program that can read the RDB and check if the stored CHS values have more heads than 16 or more Blocks/Sectors per track than 63.
Update: A related issue submitted by Thomas is that some SD/CF cards with very poor firmware forget that the first LBA block is number 0, and consequently tries to access one block too far.
This would also fail with the same consequences when used in LBA capable system
