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Should i change size of running pool to increase capacity?

I have a cluster with 4 nodes, each node has 4 x 960GB Enterprise SSD and i created pool with size =4 ;

I think each file will have 4 copies, so I only have 4 TB of Capacity, now I want to reduce the pools's size to increase capacity while pools are running without loss data, is it possible?

Thank for your advices

Best regards

Phan Long

Yes you can decrease the pool size from 4 to 3 without problem

Thank for your help, I've changed size of cephfs_data from 4 to 3 and saved, but it's status changed from active to inactive, because my petasan providing storage for 200 running VPSs so it make me very worry
So I changed size of cephfs_data from 3 back to 4 and saved, it's status changed back to be actived again.

Thank you

The cluster will go inactive while it rebalances and removes the duplicate shards. This is normal and expected and a large maintenance window it needed.

For your cluster, I would add more drives per node if possible (ram and cpu cores depending) or add another node or two. The beauty of a storage cluster is being able to expand as needed and petasan makes only one requirement that you have the same minimum number  network connections (disable the extras if your not using them).

It is also possible to migrate the VMs storage off the cluster, rebuild the cluster to the new duplication setting and migrate back. We have done this with ours a few times and it works well as the VM does not need to shutdown (at least with Citrix Xenserver) to do this, though 200VPS's will take some time to do this as you do not want to move more than what your cluster and the temporary NAS can handle for extra load. You may even need to run a couple NAS boxes during this migration to handle the working load of your VPS's.