Thank you Greg, much appreciated. I'll test with the crush tool to see if it complains about this new layout.
George On Mon, Feb 22, 2016 at 3:19 PM, Gregory Farnum <[email protected]> wrote: > On Mon, Feb 22, 2016 at 9:29 AM, George Mihaiescu <[email protected]> > 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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