Changes

In contrast, global persistent volumes are provided cluster-wide and are accessible from any node (managed internally with rook-ceph). They reside on SSDs and thus should be reasonably fast, however, depending on where the volume ends up, data will probably be transferred across the network to/from the node. Thus, they are slower than local-ssd, but leave you considerably more flexible, as they do not require pods to run on specific nodes. Also, there is no upper limit constraint on maximum size except for physical oneslimitations. Currently, there is a total of 20 TB of cluster-wide SSD storage, which we plan to increase considerably in the near future.