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
maxConcurrentSnapshotFileDownloadsPerNode,
                            INDICES_RECOVERY_MAX_CONCURRENT_SNAPSHOT_FILE_DOWNLOADS.getKey(),
                            maxConcurrentSnapshotFileDownloads
                        )
                    );
                }
            }
            @Override
            public Iterator<Setting<?>> settings() {
                return dependencies.iterator();
            }
        },
        Setting.Property.Dynamic,
        Setting.Property.NodeScope
    );
    public static final ByteSizeValue DEFAULT_CHUNK_SIZE = new ByteSizeValue(512, ByteSizeUnit.KB);
    private volatile ByteSizeValue maxBytesPerSec;
    private volatile int maxConcurrentFileChunks;
    private volatile int maxConcurrentOperations;
    private volatile SimpleRateLimiter rateLimiter;
    private volatile TimeValue retryDelayStateSync;
    private volatile TimeValue retryDelayNetwork;
    private volatile TimeValue activityTimeout;
    private volatile TimeValue internalActionTimeout;
    private volatile TimeValue internalActionRetryTimeout;
    private volatile TimeValue internalActionLongTimeout;
    private volatile boolean useSnapshotsDuringRecovery;
    private final boolean nodeBandwidthSettingsExist;
    private volatile int maxConcurrentSnapshotFileDownloads;
    private volatile int maxConcurrentSnapshotFileDownloadsPerNode;