X-Git-Url: https://gerrit.opnfv.org/gerrit/gitweb?a=blobdiff_plain;f=src%2Fceph%2Fdoc%2Frados%2Foperations%2Fpg-concepts.rst;fp=src%2Fceph%2Fdoc%2Frados%2Foperations%2Fpg-concepts.rst;h=0000000000000000000000000000000000000000;hb=7da45d65be36d36b880cc55c5036e96c24b53f00;hp=636d6bf9a1e5b5b933769e1424488842a198c551;hpb=691462d09d0987b47e112d6ee8740375df3c51b2;p=stor4nfv.git diff --git a/src/ceph/doc/rados/operations/pg-concepts.rst b/src/ceph/doc/rados/operations/pg-concepts.rst deleted file mode 100644 index 636d6bf..0000000 --- a/src/ceph/doc/rados/operations/pg-concepts.rst +++ /dev/null @@ -1,102 +0,0 @@ -========================== - Placement Group Concepts -========================== - -When you execute commands like ``ceph -w``, ``ceph osd dump``, and other -commands related to placement groups, Ceph may return values using some -of the following terms: - -*Peering* - The process of bringing all of the OSDs that store - a Placement Group (PG) into agreement about the state - of all of the objects (and their metadata) in that PG. - Note that agreeing on the state does not mean that - they all have the latest contents. - -*Acting Set* - The ordered list of OSDs who are (or were as of some epoch) - responsible for a particular placement group. - -*Up Set* - The ordered list of OSDs responsible for a particular placement - group for a particular epoch according to CRUSH. Normally this - is the same as the *Acting Set*, except when the *Acting Set* has - been explicitly overridden via ``pg_temp`` in the OSD Map. - -*Current Interval* or *Past Interval* - A sequence of OSD map epochs during which the *Acting Set* and *Up - Set* for particular placement group do not change. - -*Primary* - The member (and by convention first) of the *Acting Set*, - that is responsible for coordination peering, and is - the only OSD that will accept client-initiated - writes to objects in a placement group. - -*Replica* - A non-primary OSD in the *Acting Set* for a placement group - (and who has been recognized as such and *activated* by the primary). - -*Stray* - An OSD that is not a member of the current *Acting Set*, but - has not yet been told that it can delete its copies of a - particular placement group. - -*Recovery* - Ensuring that copies of all of the objects in a placement group - are on all of the OSDs in the *Acting Set*. Once *Peering* has - been performed, the *Primary* can start accepting write operations, - and *Recovery* can proceed in the background. - -*PG Info* - Basic metadata about the placement group's creation epoch, the version - for the most recent write to the placement group, *last epoch started*, - *last epoch clean*, and the beginning of the *current interval*. Any - inter-OSD communication about placement groups includes the *PG Info*, - such that any OSD that knows a placement group exists (or once existed) - also has a lower bound on *last epoch clean* or *last epoch started*. - -*PG Log* - A list of recent updates made to objects in a placement group. - Note that these logs can be truncated after all OSDs - in the *Acting Set* have acknowledged up to a certain - point. - -*Missing Set* - Each OSD notes update log entries and if they imply updates to - the contents of an object, adds that object to a list of needed - updates. This list is called the *Missing Set* for that ````. - -*Authoritative History* - A complete, and fully ordered set of operations that, if - performed, would bring an OSD's copy of a placement group - up to date. - -*Epoch* - A (monotonically increasing) OSD map version number - -*Last Epoch Start* - The last epoch at which all nodes in the *Acting Set* - for a particular placement group agreed on an - *Authoritative History*. At this point, *Peering* is - deemed to have been successful. - -*up_thru* - Before a *Primary* can successfully complete the *Peering* process, - it must inform a monitor that is alive through the current - OSD map *Epoch* by having the monitor set its *up_thru* in the osd - map. This helps *Peering* ignore previous *Acting Sets* for which - *Peering* never completed after certain sequences of failures, such as - the second interval below: - - - *acting set* = [A,B] - - *acting set* = [A] - - *acting set* = [] very shortly after (e.g., simultaneous failure, but staggered detection) - - *acting set* = [B] (B restarts, A does not) - -*Last Epoch Clean* - The last *Epoch* at which all nodes in the *Acting set* - for a particular placement group were completely - up to date (both placement group logs and object contents). - At this point, *recovery* is deemed to have been - completed.