Re: copies= option

[Brendan Hide <brendan@swiftspirit.co.za>]

On 2014/05/04 05:27 AM, Duncan wrote:
> Russell Coker posted on Sun, 04 May 2014 12:16:54 +1000 as excerpted:
>
>> Are there any plans for a feature like the ZFS copies= option?
>>
>> I'd like to be able to set copies= separately for data and metadata.  In
>> most cases RAID-1 provides adequate data protection but I'd like to have
>> RAID-1 and copies=2 for metadata so that if one disk dies and another
>> has some bad sectors during recovery I'm unlikely to lose metadata.
> Hugo's the guy with the better info on this one, but until he answers...
>
> The zfs license issues mean it's not an option for me and I'm thus not
> familiar with its options in any detail, but if I understand the question
> correctly, yes.
>
> And of course since btrfs treats data and metadata separately, it's
> extremely unlikely that any sort of copies= option wouldn't be separately
> configurable for each.
>
> There was a discussion of a very nice multi-way-configuration schema that
> I deliberately stayed out of as both a bit above my head and far enough
> in the future that I didn't want to get my hopes up too high about it
> yet.  I already want N-way-mirroring so bad I can taste it, and this was
> that and way more... if/when it ever actually gets coded and committed to
> the mainline kernel btrfs.  As I said, Hugo should have more on it, as he
> was active in that discussion as it seemed to line up perfectly with his
> area of interest.
>
The simple answer is yes, this is planned. As Duncan implied, however, 
it is not on the immediate roadmap. Internally we appear to be referring 
to this feature as "N-way redundancy" or "N-way mirroring".

My understanding is that the biggest hurdle before the primary devs will 
look into N-way redundancy is to finish the Raid5/6 implementation to 
include self-healing/scrubbing support - a critical issue before it can 
be adopted further.

-- 
__________
Brendan Hide
http://swiftspirit.co.za/
http://www.webafrica.co.za/?AFF1E97