Hi James, This happens usually when the storage platform and applications are in segmented networks. For example, in a cluster with multiple RGW instances, if we could know the which RGW instance is the closest to primary copy, then we can do more efficient local read/write through some particular deployment. There's one feature in Openstack Swift [1] which is able to provide the location of objects inside a cluster.
Thanks, -yuan [1] https://github.com/openstack/swift/blob/master/swift/common/middleware/list_endpoints.py -----Original Message----- From: James (Fei) Liu-SSI [mailto:[email protected]] Sent: Saturday, May 9, 2015 1:40 AM To: Zhou, Yuan; Ceph Development Cc: Cohen, David E; Yu, Zhidong Subject: RE: libcrush.so Hi Yuan, Very interesting. Would be possible to know why application needs to access the cursh map directly instead of accessing through ceph tool? Regards, James -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Zhou, Yuan Sent: Thursday, May 07, 2015 6:29 PM To: Ceph Development Cc: Cohen, David E; Yu, Zhidong Subject: libcrush.so Ceph use crush algorithm to provide the mapping of objects to OSD servers. This is great for clients so they could talk to with these OSDs directly. However there are some scenarios where the application needs to access the crush map, for load-balancing as an example. Currently Ceph doesn't provides any API to render the layout. If your application needs to access the crush map you'll going to rely on the command 'ceph osd map pool_name obj_name'. With this libcrush.so we could let the application to choose which nodes to access. The other advantage is we could provide some other bindings(python, go) based on this also. >From the git log we find libcrush was there before but removed out since >Argonaut. Can anyone kindly share us the background of this change? Thanks, -yuan -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
