doc: Fix misleading overlay settting in Cache Tier

set-overlay is needed in either writeback or readonly mode of Cache
Tier setup.

Signed-off-by: Yuan Zhou <yuan.zhou@intel.com>

diff --git a/doc/rados/operations/cache-tiering.rst b/doc/rados/operations/cache-tiering.rst
index 70dbeeecf4a46a76d265dc098913e04a98fa5581..bf6f8e556502515f17f8e9f107f1986b49a54710 100644 (file)
--- a/doc/rados/operations/cache-tiering.rst
+++ b/doc/rados/operations/cache-tiering.rst
@@ -139,7 +139,7 @@ For example::
 
        ceph osd tier cache-mode hot-storage writeback
 
-Writeback cache tiers overlay the backing storage tier, so they require one
+The cache tiers overlay the backing storage tier, so they require one
 additional step: you must direct all client traffic from the storage pool to 
 the cache pool. To direct client traffic directly to the cache pool, execute 
 the following::