calculateClusterCapacity multiplies advertised volume slots by the
volume size limit. Slot counts are an admission bound rather than a
capacity measurement — an explicit -max can be set higher than the
volumes a disk actually fills — so a small disk can report more total
and available capacity than it physically has. Bound both numbers by
the per-disk filesystem counters the volume server already reports in
its heartbeat, falling back to the slot estimate only when they are
absent.
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Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
