Document increasing the disk size or adding a second disk to a microceph node.

[eedgar]

Please provide documentation on the best practices for adding disks to the cluster.

for example many people might have a small 3 node cluster and just want to add disks to all 3 nodes .. or they may be in a lab and realize they want to increase the disk sizes instead of starting from scratch. Please provide the best practices way of doing so.

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