Re: Help with space

Brendan Hide
2014-05-02T09:28:28Z

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.duncan@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.

--
__________
Brendan Hide