Thank you Greg, much appreciated.
I'll test with the crush tool to see if it complains about this new layout.On Mon, Feb 22, 2016 at 3:19 PM, Gregory Farnum <gfarnum@xxxxxxxxxx> wrote:
On Mon, Feb 22, 2016 at 9:29 AM, George Mihaiescu <lmihaiescu@xxxxxxxxx> wrote:
> Hi,
>
> We have a fairly large Ceph cluster (3.2 PB) that we want to expand and we
> would like to get your input on this.
>
> The current cluster has around 700 OSDs (4 TB and 6 TB) in three racks with
> the largest pool being rgw and using a replica 3.
> For non-technical reasons (budgetary, etc) we are considering getting three
> more racks, but initially adding only two storage nodes with 36 x 8 TB
> drives in each, which will basically cause the rack weights to be imbalanced
> (three racks with weight around a 1000 and 288 OSDs, and three racks with
> weight around 500 but only 72 OSDs)
>
> The one replica per rack CRUSH rule will cause existing data to be
> re-balanced among all six racks, with OSDs in the new racks getting only a
> proportionate amount of replicas.
>
> Do you see any possible problems with this approach? Should Ceph be able to
> properly rebalance the existing data among racks with imbalanced weights?
>
> Thank you for your input and please let me know if you need additional info.
This should be okay; you have multiple racks in each size and aren't
trying to replicate a full copy to each rack individually. You can
test it ahead of time with the crush tool, though:
http://docs.ceph.com/docs/master/man/8/crushtool/
It may turn out you're using old tunables and want to update them
first or something.
-Greg
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