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diff --git a/doc/radosgw/orphans.rst b/doc/radosgw/orphans.rst new file mode 100644 index 00000000..9a77d60d --- /dev/null +++ b/doc/radosgw/orphans.rst @@ -0,0 +1,115 @@ +================================== +Orphan List and Associated Tooling +================================== + +.. version added:: Luminous + +.. contents:: + +Orphans are RADOS objects that are left behind after their associated +RGW objects are removed. Normally these RADOS objects are removed +automatically, either immediately or through a process known as +"garbage collection". Over the history of RGW, however, there may have +been bugs that prevented these RADOS objects from being deleted, and +these RADOS objects may be consuming space on the Ceph cluster without +being of any use. From the perspective of RGW, we call such RADOS +objects "orphans". + +Orphans Find -- DEPRECATED +-------------------------- + +The `radosgw-admin` tool has/had three subcommands to help manage +orphans, however these subcommands are (or will soon be) +deprecated. These subcommands are: + +:: + # radosgw-admin orphans find ... + # radosgw-admin orphans finish ... + # radosgw-admin orphans list-jobs ... + +There are two key problems with these subcommands, however. First, +these subcommands have not been actively maintained and therefore have +not tracked RGW as it has evolved in terms of features and updates. As +a result the confidence that these subcommands can accurately identify +true orphans is presently low. + +Second, these subcommands store intermediate results on the cluster +itself. This can be problematic when cluster administrators are +confronting insufficient storage space and want to remove orphans as a +means of addressing the issue. The intermediate results could strain +the existing cluster storage capacity even further. + +For these reasons "orphans find" has been deprecated. + +Orphan List +----------- + +Because "orphans find" has been deprecated, RGW now includes an +additional tool -- 'rgw-orphan-list'. When run it will list the +available pools and prompt the user to enter the name of the data +pool. At that point the tool will, perhaps after an extended period of +time, produce a local file containing the RADOS objects from the +designated pool that appear to be orphans. The administrator is free +to examine this file and the decide on a course of action, perhaps +removing those RADOS objects from the designated pool. + +All intermediate results are stored on the local file system rather +than the Ceph cluster. So running the 'rgw-orphan-list' tool should +have no appreciable impact on the amount of cluster storage consumed. + +WARNING: Experimental Status +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The 'rgw-orphan-list' tool is new and therefore currently considered +experimental. The list of orphans produced should be "sanity checked" +before being used for a large delete operation. + +WARNING: Specifying a Data Pool +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +If a pool other than an RGW data pool is specified, the results of the +tool will be erroneous. All RADOS objects found on such a pool will +falsely be designated as orphans. + +WARNING: Unindexed Buckets +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +RGW allows for unindexed buckets, that is buckets that do not maintain +an index of their contents. This is not a typical configuration, but +it is supported. Because the 'rgw-orphan-list' tool uses the bucket +indices to determine what RADOS objects should exist, objects in the +unindexed buckets will falsely be listed as orphans. + + +RADOS List +---------- + +One of the sub-steps in computing a list of orphans is to map each RGW +object into its corresponding set of RADOS objects. This is done using +a subcommand of 'radosgw-admin'. + +:: + # radosgw-admin bucket radoslist [--bucket={bucket-name}] + +The subcommand will produce a list of RADOS objects that support all +of the RGW objects. If a bucket is specified then the subcommand will +only produce a list of RADOS objects that correspond back the RGW +objects in the specified bucket. + +Note: Shared Bucket Markers +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Some administrators will be aware of the coding schemes used to name +the RADOS objects that correspond to RGW objects, which include a +"marker" unique to a given bucket. + +RADOS objects that correspond with the contents of one RGW bucket, +however, may contain a marker that specifies a different bucket. This +behavior is a consequence of the "shallow copy" optimization used by +RGW. When larger objects are copied from bucket to bucket, only the +"head" objects are actually copied, and the tail objects are +shared. Those shared objects will contain the marker of the original +bucket. + +.. _Data Layout in RADOS : ../layout +.. _Pool Placement and Storage Classes : ../placement |