[Bug 220343] The manual page for mpt should inform about disk size limitations of most/all supported controllers

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=220343

            Bug ID: 220343
           Summary: The manual page for mpt should inform about disk size
                    limitations of most/all supported controllers
           Product: Documentation
           Version: Latest
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: Documentation
          Assignee: freebsd-doc at FreeBSD.org
          Reporter: sebastian at rostwald.de

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.


Draft/suggestion:

----

WARNING

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.

----


-- 
Regards,
Sebastian

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