import ceph octopus 15.2.17

[ceph.git] / ceph / doc / start / hardware-recommendations.rst

diff --git a/ceph/doc/start/hardware-recommendations.rst b/ceph/doc/start/hardware-recommendations.rst
index 42a0e1e57524576a990b02738d689a3fa70dd173..9086349d6a2c5da36d3c77522b0decedbe9ac53a 100644 (file)
--- a/ceph/doc/start/hardware-recommendations.rst
+++ b/ceph/doc/start/hardware-recommendations.rst
@@ -63,29 +63,31 @@ Memory
 ======
 
 Bluestore uses its own memory to cache data rather than relying on the
-operating system page cache.  In bluestore you can adjust the amount of memory
-the OSD attempts to consume with the ``osd_memory_target`` configuration
-option.
+operating system's page cache. In Bluestore you can adjust the amount of memory
+that the OSD attempts to consume by changing the `osd_memory_target`
+configuration option.
 
-- Setting the osd_memory_target below 2GB is typically not recommended (it may
-  fail to keep the memory that low and may also cause extremely slow performance.
+- Setting the `osd_memory_target` below 2GB is typically not
+  recommended (Ceph may fail to keep the memory consumption under 2GB and 
+  this may cause extremely slow performance).
 
 - Setting the memory target between 2GB and 4GB typically works but may result
   in degraded performance as metadata may be read from disk during IO unless the
   active data set is relatively small.
 
-- 4GB is the current default osd_memory_target size and was set that way to try
-  and balance memory requirements and OSD performance for typical use cases.
+- 4GB is the current default `osd_memory_target` size. This default
+  was chosen for typical use cases, and is intended to balance memory
+  requirements and OSD performance.
 
-- Setting the osd_memory_target higher than 4GB may improve performance when
-  there are many (small) objects or large (256GB/OSD or more) data sets being
-  processed.
+- Setting the `osd_memory_target` higher than 4GB can improve
+  performance when there many (small) objects or when large (256GB/OSD 
+  or more) data sets are processed.
 
 .. important:: The OSD memory autotuning is "best effort".  While the OSD may
    unmap memory to allow the kernel to reclaim it, there is no guarantee that
-   the kernel will actually reclaim freed memory within any specific time
-   frame.  This is especially true in older versions of Ceph where transparent
-   huge pages can prevent the kernel from reclaiming memory freed from
+   the kernel will actually reclaim freed memory within a specific time
+   frame. This applies especially in older versions of Ceph, where transparent
+   huge pages can prevent the kernel from reclaiming memory that was freed from
    fragmented huge pages. Modern versions of Ceph disable transparent huge
    pages at the application level to avoid this, though that still does not
    guarantee that the kernel will immediately reclaim unmapped memory.  The OSD
@@ -95,9 +97,10 @@ option.
    kernel.  That value may be more or less than needed depending on the exact
    configuration of the system.
 
-When using the legacy FileStore backend, the page cache is used for caching
-data, so no tuning is normally needed, and the OSD memory consumption is
-generally related to the number of PGs per daemon in the system.
+When using the legacy FileStore back end, the page cache is used for caching
+data, so no tuning is normally needed. When using the legacy FileStore backend,
+the OSD memory consumption is related to the number of PGs per daemon in the
+system.
 
 
 Data Storage