Adding upstream version 18.2.2.upstream/18.2.2

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 39 insertions, 0 deletions

diff --git a/doc/rados/configuration/journal-ref.rst b/doc/rados/configuration/journal-ref.rst
new file mode 100644
index 000000000..5ce5a5e2d
--- /dev/null
+++ b/doc/rados/configuration/journal-ref.rst
@@ -0,0 +1,39 @@
+==========================
+ Journal Config Reference
+==========================
+.. warning:: Filestore has been deprecated in the Reef release and is no longer supported.
+.. index:: journal; journal configuration
+
+Filestore OSDs use a journal for two reasons: speed and consistency.  Note
+that since Luminous, the BlueStore OSD back end has been preferred and default.
+This information is provided for pre-existing OSDs and for rare situations where
+Filestore is preferred for new deployments.
+
+- **Speed:** The journal enables the Ceph OSD Daemon to commit small writes 
+  quickly. Ceph writes small, random i/o to the journal sequentially, which 
+  tends to speed up bursty workloads by allowing the backing file system more 
+  time to coalesce writes. The Ceph OSD Daemon's journal, however, can lead 
+  to spiky performance with short spurts of high-speed writes followed by 
+  periods without any write progress as the file system catches up to the 
+  journal.
+
+- **Consistency:** Ceph OSD Daemons require a file system interface that 
+  guarantees atomic compound operations. Ceph OSD Daemons write a description 
+  of the operation to the journal and apply the operation to the file system. 
+  This enables atomic updates to an object (for example, placement group 
+  metadata). Every few seconds--between ``filestore max sync interval`` and
+  ``filestore min sync interval``--the Ceph OSD Daemon stops writes and 
+  synchronizes the journal with the file system, allowing Ceph OSD Daemons to 
+  trim operations from the journal and reuse the space. On failure, Ceph 
+  OSD Daemons replay the journal starting after the last synchronization 
+  operation.
+
+Ceph OSD Daemons recognize the following journal settings: 
+
+.. confval:: journal_dio
+.. confval:: journal_aio
+.. confval:: journal_block_align
+.. confval:: journal_max_write_bytes
+.. confval:: journal_max_write_entries
+.. confval:: journal_align_min_size
+.. confval:: journal_zero_on_create