Check pool-index for invalid setups (#16501)

cmd/erasure-server-pool-rebalance.go

@@ -133,6 +133,11 @@ func (z *erasureServerPools) initRebalanceMeta(ctx context.Context, buckets []st
 	}, len(z.serverPools))
 	var totalCap, totalFree uint64
 	for _, disk := range si.Disks {
+		// Ignore invalid.
+		if disk.PoolIndex < 0 || len(diskStats) <= disk.PoolIndex {
+			// https://github.com/minio/minio/issues/16500
+			continue
+		}
 		totalCap += disk.TotalSpace
 		totalFree += disk.AvailableSpace