Most (if not all?) controllers supported by the mpt driver have firmware- and/or hardware-induced limitations on their supported disk/array/LUN size - mostly <2TB. As these limitations are well below typical sizes of modern hard drives, it would be sensible to inform the user about these limitations in the manual page.
While most controllers truncate the usable/reported size to the supported size, some might wrap around and cause serious data corruption. See for example the 3ware 7000/8000 series in this archived KB article: http://web.archive.org/web/20120326110817/http://kb.lsi.com:80/KnowledgebaseArticle16481.aspx
From my own experiences, behaviour of many controllers with such limitations upon attaching bigger disks is best described as "undefined" - I've seen anything from not recognizing/reporting the disks, locking up at boot to severe data loss when reaching the supported size limit.
Due to the possibility of data loss on controllers that wrap around address space, I suggest adding the information about these limitations and possible data loss within a WARNING section of the manual page.
Most controllers supported by the mpt driver suffer from limitations on supported disk size (mostly <2TB). While *most* controllers will only truncate usable disk size, others might behave unexpectedly and cause severe data loss. Refer to the specifications of your chipset and firmware version for information about supported disk size.
Created attachment 184353 [details]
patch for the mpt manpage, adding warning about disk size limitations
It's a little late, but I'll take this.
Incidentally, is it okay to credit you as "Sebastian Oswald <sebastian at rostwald.de>" in the commit?
A commit in branch main references this bug:
Author: Sebastian Oswald <sebastian at rostwald.de>
AuthorDate: 2021-01-16 23:27:43 +0000
Commit: Daniel Ebdrup Jensen <debdrup@FreeBSD.org>
CommitDate: 2021-01-16 23:41:59 +0000
mpt.4: Warn about unexpected behaviour on older controllers
Older controllers have errata which causes the disk controller to wrap
data to other LBAs, causing data to be overwritten. 
While here, fix a small typo.
Submitted by: Sebastian Oswald <sebastian at rostwald.de>
Reviewed by: 0mp
Event: January 2021 Bugathon
Differential Revision: <https://reviews.freebsd.org/D28201
share/man/man4/mpt.4 | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
Thank you for your attention to detail. :)
(In reply to Daniel Ebdrup Jensen from comment #2)
Better late than never ;)
> Incidentally, is it okay to credit you as "Sebastian Oswald <sebastian at
> rostwald.de>" in the commit?
Yes, that's ok, thanks!