We limit the number of concurrent blob downloads per node and per recovery, but if a user configures too many concurrent recoveries they may run out of per-node download permits which yields the following message:

> Unable to acquire permit to use snapshot files during recovery, this recovery will recover index files from the source node. Ensure snapshot files can be used during recovery by setting [indices.recovery.max_concurrent_snapshot_file_downloads] to be no greater than [25]

The `[25]` here is wrong, the 25 permits are shared across all inbound recoveries so we should divide the suggested value by `cluster.routing.allocation.node_concurrent_incoming_recoveries`. In extreme cases the user may have configured so many concurrent recoveries that the only reasonable limit is zero, and in that case we should suggest setting `indices.recovery.use_snapshots: false` instead.


server/src/main/java/org/elasticsearch/indices/recovery/RecoverySettings.java
if (ByteSizeValue.MINUS_ONE.equals(value)) {
                return value;
            }
            if (value.getBytes() <= 0L) {
                throw new IllegalArgumentException(
                    "Failed to parse value ["
                        + s
                        + "] for bandwidth setting ["
                        + key
                        + "], must be > ["
                        + ByteSizeValue.ZERO.getStringRep()
                        + ']'
                );
            }
            if (value.getBytes() >= Long.MAX_VALUE) {
                throw new IllegalArgumentException(
                    "Failed to parse value ["
                        + s
                        + "] for bandwidth setting ["
                        + key
                        + "], must be < ["
                        + ByteSizeValue.ofBytes(Long.MAX_VALUE).getStringRep()
                        + ']'
                );
            }
            return value;
        }, Property.NodeScope);
    }
    /**
     * Operator-defined factors have a value in (0.0, 1.0]