On Thu, Nov 1, 2012 at 10:33 PM, Gandalf Corvotempesta <gandalf.corvotempesta@xxxxxxxxx> wrote: > 2012/11/1 Mark Nelson <mark.nelson@xxxxxxxxxxx>: >> It will do that for a while, based on how you've tweaked the flush intervals >> and various journal settings to determine how much data ceph will allow to >> hang out in the journal while still accepting new requests. > > Ceph is not able to write to both journal and disks simultaneously? > For example, by using SSD for operating system and journal, we will be > able to have not least than 100GB of journal that is a large amount of > data wrote at SSD speed. > > When ceph has to flush this data to disks, will stop to write more > data to journal? No, of course it will flush data to the disk at the same time as it will take writes to the journal. However, if you have a 1GB journal that writes at 200MB/s and a backing disk that writes at 100MB/s, and you then push 200MB/s through long enough that the journal fills up, then you will slow down to writing at 100MB/s because that's as fast as Ceph can fill up the backing store, and the journal is no longer buffering. -Greg -- 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
