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I think you may have two separate issues.
Quote:
Originally Posted by Smith
What I have is a genuinely NTFS formatted 4TB drive....
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When I saw this, I thought, "uh oh". That's because MBR partition tables are limited to 2TB, and disks larger appear in the MBR as 2TB. As mentioned in FAQ 14.8, this is not a problem for OpenBSD, as the OpenBSD disklabel doesn't have this restriction. However, you are using a disk that contains only a foreign filesystem, and then a "virtual" disklabel based on the MBR, which is of course limited to 2TB.
Setting the right partition size: I recommend creating a physical disklabel on the drive, so that OpenBSD can address the actual size of the NTFS partition. e.g.: create a small OpenBSD MBR partition of type A6 on the drive, to house the disklabel. This can be a very small partition, such as 1MB in size. Then use disklabel(8) to correctly map the "real" NTFS partition by starting sector and size into the physical disklabel.
Sector size may be an issue: While it may seem simple to humans to use a larger sector size, since the 1970s fixed block architecture drives have been using 512-byte sectors, and 4096-byte sectors are "brand new". There's a lot of OS and driver code that does not support 4096-byte sector drives.
Therefore, I would not be surprised if the built-in NTFS driver in OpenBSD might not support 4096-byte sector devices. You should test this with a small NTFS partition, to determine if this is a problem before resolving the 2TB limitation imposed by MBR partitioning. In the event that the built-in NTFS driver does not support 4096-byte sectors, then you might consider trying the
ntfs_3g package, which uses OpenBSD's FUSE implementation. Along with the possibility of supporting 4096-byte sectors, this NTFS driver also supports write access.