Bug 220343

Summary: The manual page for mpt(4) should inform about disk size limitations of most/all supported controllers
Product: Documentation Reporter: Sebastian Oswald (sko) <sebastian>
Component: Manual PagesAssignee: freebsd-bugs (Nobody) <bugs>
Status: New ---    
Severity: Affects Some People CC: doc
Priority: --- Keywords: patch
Version: Latest   
Hardware: Any   
OS: Any   
Attachments:
Description Flags
patch for the mpt manpage, adding warning about disk size limitations none

Description Sebastian Oswald (sko) 2017-06-28 19:01:26 UTC
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:

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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.

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Regards,
Sebastian
Comment 1 Sebastian Oswald (sko) 2017-07-14 13:41:29 UTC
Created attachment 184353 [details]
patch for the mpt manpage, adding warning about disk size limitations