Re: [PATCH 0/5] [RFC] RAID-level terminology change

[Roger Binns <rogerb@rogerbinns.com>]

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On 26/03/13 21:27, Brendan Hide wrote:

> On 11/03/13 02:21, Roger Binns wrote:
>> Why does all data have to be rewritten?  Why does every piece of data
>> have to have exactly the same storage parameters in terms of 
>> non-redundancy/performance/striping options?

> This is a good point. You don't necessarily have to rewrite everything
> all at once so the performance penalty is not necessarily that bad.
> More importantly, some "restripe" operations actually don't need much
> change on-disk (in theory).

Note that is not what I was describing.  What I meant was that if I put
10GB of data onto 100GB of space that btrfs is free to go above and beyond
the minimums, and to do so differently for different pieces of data.  For
example  btrfs could make 6 copies of files beginning with 'a', 10 of
files beginning with 'c' and 274 of all others.  Obviously that is a bad
heuristic, but anything it deems useful for all that unused space is fine
by me, and there is absolutely no need for every block to have exactly the
same parameters all others.

Roger



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