It doesn't matter what your failure domain is, the data movement is significant to change your crush rules to use device classes. You can attempt to mitigate this by creating new, duplicate rules and change 1 pool at a time to start using them. In that way you can somewhat control the backfilling unless you have 1 pool with a vast majority of the data.
On Thu, Feb 1, 2018, 5:31 AM Konstantin Shalygin <k0ste@xxxxxxxx> wrote:
> We had a MASSIVE data movement upon changing the crush rules to device
> class based one. I'm not sure about the exact reasons, but I assume that
> the order of hosts in the crush tree has changed (hosts are ordered
> lexically now...), which resulted in about 80% of data being moved around.
What is you failure domain? Host I think?
This cluster failure domain is rack.
k
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