On Wed, 2018-05-30 at 09:37 +0200, Supriti Singh wrote:

Hello,

Recently Jeff introduced few more recovery backends: rados_kv, rados_ng and rados_cluster. I want to understand which recovery backend should be used for which use case? From design point of view what are differences among these three recovery backend?

Thanks, Supriti

rados_kv: This is the original rados recovery backend that uses a key- value store. It has support for "takeover" operations: merging one recovery database into another such that another cluster node could take over addresses that were hosted on another node. Note that this recovery backend may not survive crashes that occur _during_ a grace period. If it crashes and then crashes again during the grace period, the server is likely to fail to allow any clients to recover (the db will be trashed). rados_ng: a more resilient rados_kv backend. This one does not support takeover operations, but it should properly survive crashes that occur during the grace period. rados_cluster: the new (experimental) clustered recovery backend. This one also does not support address takeover, but should be resilient enough to handle crashes that occur during the grace period. FWIW, the semantics for fs vs. fs_ng are similar. fs doesn't survive crashes that occur during the grace period either. Unless you're trying to use the dbus "grace" command to initiate address takeover in an active/active cluster, you probably want rados_ng for now. -- Jeff Layton <jlayton@poochiereds.net>