doc: add docs for rbd_default_order

Adds documentation how to change default rbd object size. With the
previous option `--order` it was easy to guess the config name for the
default value, with the current option name `--object-size` thats hard
to guess.

Also extends the documentation for rbd_default_order to include
* how object-size is derived from the configured value
* allowed range of the value

In the first version of this commit I also added min and max for this
parameter (12/25, matching the object size range in `man 8
rbd`/Striping/object-size), but this made some tests fail, since some
seem to set values outside this range (and probably are fine since
included for some time already). To have this a doc-change only, I
removed the range.

Signed-off-by: Mara Sophie Grosch <littlefox@lf-net.org>

diff --git a/doc/man/8/rbd.rst b/doc/man/8/rbd.rst
index 93483586caf5a93d5b25fed0b57cfc767140d2ea..1f6c841f5b6bcf2e1339b2d012ffaf9450eaf288 100644 (file)
--- a/doc/man/8/rbd.rst
+++ b/doc/man/8/rbd.rst
@@ -81,6 +81,9 @@ Parameters
    nearest power of two; if no suffix is given, unit B is assumed.  The default
    object size is 4M, smallest is 4K and maximum is 32M.
 
+   The default value can be changed with the configuration option ``rbd_default_order``,
+   which takes a power of two (default object size is ``2 ^ rbd_default_order``).
+
 .. option:: --stripe-unit size-in-B/K/M
 
    Specifies the stripe unit size in B/K/M.  If no suffix is given, unit B is

diff --git a/doc/rbd/rbd-config-ref.rst b/doc/rbd/rbd-config-ref.rst
index 2e391a217ca71d3d5949e9a2c1cb1ba098f11ff9..77e570de84f5b5557361af12550316367adce887 100644 (file)
--- a/doc/rbd/rbd-config-ref.rst
+++ b/doc/rbd/rbd-config-ref.rst
@@ -9,6 +9,7 @@ Generic IO Settings
 
 .. confval:: rbd_compression_hint
 .. confval:: rbd_read_from_replica_policy
+.. confval:: rbd_default_order
 
 Cache Settings
 =======================

diff --git a/src/common/options/rbd.yaml.in b/src/common/options/rbd.yaml.in
index 14c782df9662c045ec51b8c1e4bd8ce8eceeb6a3..328fa43d18c41a578bc135fe4d944c9621c6bead 100644 (file)
--- a/src/common/options/rbd.yaml.in
+++ b/src/common/options/rbd.yaml.in
@@ -481,6 +481,9 @@ options:
   type: uint
   level: advanced
   desc: default order (data block object size) for new images
+  long_desc: This configures the default object size for new images. The value is used as a
+    power of two, meaning ``default_object_size = 2 ^ rbd_default_order``. Configure a value
+    between 12 and 25 (inclusive), translating to 4KiB lower and 32MiB upper limit.
   default: 22
   services:
   - rbd