On Fri, 29 Jan 2016, Guang Yang wrote: > Hi Sage, > I found a thread discussing whether we could turn on disk cache with > new kernel or not - > http://www.spinics.net/lists/ceph-devel/msg06173.html > > From within that thread, you mentioned that since the fsync/fdatasync > would flush the disk cache as well, we could actually turn on the > cache without worrying about the data safety. Yeah, any vaguely modern kernel will do a proper flush to the device; no need to worry about the disk cache. > Is that true if journal_dio is being used (by default), in which case > O_DIRECT | O_DSYNC is being used to write journal rather than > fsync(2)? Right. O_DSYNC triggers a flush at the SCSI (or virtio) level, so these journal [A]IOs are fully synchronous all the way to the platter. sage -- 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
