[Re-added the list.] On Wed, Jan 22, 2014 at 4:15 AM, Tim Zhang <cofol1986@xxxxxxxxx> wrote: > Hi Gregory, > I find in the src code:ReplicatedPG.cc in the function do_pg_op() I see this > two flag: > CEPH_OSD_FLAG_ACK and CEPH_OSD_FLAG_ONDISK, > what's the differenrence between this two flag? In some circumstances (when running btrfs, basically) the OSD will tell clients about two separate events: 1) Your operation is readable (CEPH_OSD_FLAG_ACK), 2) Your operation is safe (CEPH_OSD_FLAG_ONDISK) CEPH_OSD_FLAG_ONDISK implies CEPH_OSD_FLAG_ACK, as the OSD will delay any reads to an object with in-progress writes, and when using xfs or ext4 the data is always made durable before being readable. But clients and applications with reduced consistency requirements can use the ACK for faster operation in some cases. -Greg Software Engineer #42 @ http://inktank.com | http://ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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