doc: explain that tell bench is non-destructive

Mention that "ceph tell osd.N bench" will not overwrite data in a live
OSD, but might temporarily affect OSD performance.

Signed-off-by: Florian Haas <florian@hastexo.com>

diff --git a/doc/rados/operations/control.rst b/doc/rados/operations/control.rst
index 35feaee81f3d4359bfcba90b8745f451fdf3d2ee..293cdb005f6b94d9fdafd9f59b7974a9e3782232 100644 (file)
--- a/doc/rados/operations/control.rst
+++ b/doc/rados/operations/control.rst
@@ -286,7 +286,10 @@ Sends a repair command to OSD.N. To send the command to all OSDs, use ``*``. ::
 
 Runs a simple throughput benchmark against OSD.N, writing ``NUMBER_OF_OBJECTS``
 in write requests of ``BYTES_PER_WRITE`` each. By default, the test
-writes 1 GB in total in 4-MB increments. ::
+writes 1 GB in total in 4-MB increments.
+The benchmark is non-destructive and will not overwrite existing live
+OSD data, but might temporarily affect the performance of clients
+concurrently accessing the OSD. ::
 
        ceph tell osd.N bench [NUMER_OF_OBJECTS] [BYTES_PER_WRITE]