The Ceph Wiki (http://ceph.com/wiki/OSD_journal) does a pretty good job explaining the purpose of the journal and various modes available. What isn't clear is what happens during the failure of a journal.
With the use of btrfs enabling parallel journaling, it sounds like failure of a journal device would still enable OSD writes to occur albeit at a slower pace. In writeahead mode, failure of the journal seems like it would take all OSDs using that device for journaling offline. Is this a correct assessment? If the journal is a single point of failure to a system with potentially multiple OSDs ... it might be worth mentioning in one of the "building a cluster" or hardware pages about journal redundancy. Also, it would be nice to know what steps are required to replace a journal. (I think this is just an update of the cluster.conf with the new journal device and a restart of the OSD process, correct?) Best regards, Calvin -- 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
