On 02/05/14 10:23, Duncan wrote:
Russell Coker posted on Fri, 02 May 2014 11:48:07 +1000 as excerpted:
On Thu, 1 May 2014, Duncan <1i5t5.dun...@cox.net> wrote:
[snip]
http://www.eecs.berkeley.edu/Pubs/TechRpts/1987/CSD-87-391.pdf
Whether a true RAID-1 means just 2 copies or N copies is a matter of
opinion. Papers such as the above seem to clearly imply that RAID-1 is
strictly 2 copies of data.
Thanks for that link. =:^)
My position would be that reflects the original, but not the modern,
definition. The paper seems to describe as raid1 what would later come
to be called raid1+0, which quickly morphed into raid10, leaving the
raid1 description only covering pure mirror-raid.
Personally I'm flexible on using the terminology in day-to-day
operations and discussion due to the fact that the end-result is "close
enough". But ...
The definition of "RAID 1" is still only a mirror of two devices. As far
as I'm aware, Linux's mdraid is the only raid system in the world that
allows N-way mirroring while still referring to it as "RAID1". Due to
the way it handles data in chunks, and also due to its "rampant layering
violations", *technically* btrfs's "RAID-like" features are not "RAID".
To differentiate from "RAID", we're already using lowercase "raid" and,
in the long term, some of us are also looking to do away with "raid{x}"
terms altogether with what Hugo and I last termed as "csp notation".
Changing the terminology is important - but it is particularly non-urgent.
--
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Brendan Hide
http://swiftspirit.co.za/
http://www.webafrica.co.za/?AFF1E97
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