[Gluster-users] balancing redundancy with space utilization

[Anand Babu Periasamy]

Hi Tom,
You need unify of afr volumes.

3 copies of 8 servers is slightly odd to pair. Though you
have options..
1) 1-2-3, 4-5-6, 7-8-1
2) 1-2-3, 4-5-6, 7-8
3) 1-2-3, 2-3-4, 3-4-5 4-5-6 5-6-7 6-7-8

My recommendation is to go for 9 servers if you are looking
for 3 copies of all files. Upgrading in pairs of 3 becomes
easier at a later stage.

Please refer to this documentation:
http://www.gluster.org/docs/index.php/Unify_over_AFR

Happy Hacking,
--
Anand Babu Periasamy
GPG Key ID: 0x62E15A31
Blog [http://ab.freeshell.org]
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Tom Lahti wrote:
> Currently it would seem that AFR will simply copy everything to every 
> brick in the AFR.  If I did something like ...
> 
> volume afr-example
>    type cluster/afr
>    subvolumes brick1 brick2 brick3 brick4 brick5 brick6 brick7 brick8
> end-volume
> 
> I would wind up with 8 copies of every file.  Clearly, this is too many. 
>   What I would rather have is maybe 3 copies of each file distributed 
> randomly across 3 servers, so that I could still have 2 servers fail and 
>   have all data available, but without using up unnecessary space on the 
> other 5.  The 3 would need to be round-robined in some manner so as to 
> distribute the disk utilization.  First file goes on brick1 brick2 
> brick3, 2nd file goes on brick2 brick3 brick4, etc.
> 
> It seems that AFR used to have this with "option relicate *:3" but that 
> was removed.  The supposed replacement for that, the switch scheduler, 
> doesn't really have the same functionality.
> 
> Unless there is a undocumented form of the "option switch.case" 
> statement that I have yet to see.  Can I do "option switch.case *:3" or 
> some such?
>