Re: Replication question

[Steve Anthony <sma310@xxxxxxxxxx>]

Actually, it's more like 41TB. It's a bad idea to run at near full capacity (by default past 85%) because you need some space where Ceph can replicate data as part of its healing process in the event of disk or node failure. You'll get a health warning when you exceed this ratio.

You can use erasure coding to increase the amount of data you can store beyond 41TB, but you'll still need some replicated disk as a caching layer in front of the erasure coded pool if you're using RBD. See: http://lists.ceph.com/pipermail/ceph-users-ceph.com/2013-December/036430.html

As to how much space you can save with erasure coding, that will depend on if you're using RBD and need a cache layer and the values you set for k and m (number of data chunks and coding chunks). There's been some discussion on the list with regards to choosing those values.

-Steve

On 03/12/2015 10:07 AM, Thomas Foster wrote:

I am looking into how I can maximize my space with replication, and I am trying to understand how I can do that.

I have 145TB of space and a replication of 3 for the pool and was thinking that the max data I can have in the cluster is ~47TB in my cluster at one time..is that correct?  Or is there a way to get more data into the cluster with less space using erasure coding?  

Any help would be greatly appreciated.

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-- 
Steve Anthony
LTS HPC Support Specialist
Lehigh University
sma310@xxxxxxxxxx

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