> I do not think I understand this well. When the writeahead journal mode is > in use, would you please explain what happens to a single 4M write request? > I assume that an entry in the journal will be created for this write request > and after this entry is flushed to the journal disk, Ceph returns > successful. There should be no IO to the osd's disk. All IOs are supposed to > go to the journal disk. At a later time, Ceph will start to apply these > changes to the normal filesystem by reading from the first entry at which > its previous synchronization stops. Finally, it will read this entry and > apply this write change to the normal file system. Could you please point > out where is wrong in my understanding? Thanks, > Probably you are expecting journal to behave like cache if I understood correctly. Journals are for integrity, caches are for io speed. For block device caching you could see more on flashcache or bcache. BR, Ugis -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
