On Monday, January 28, 2013 at 9:54 AM, Ben Rowland wrote: > Hi, > > I'm considering using Ceph to create a cluster across several data > centres, with the strict requirement that writes should go to both > DCs. This seems possible by specifying rules in the CRUSH map, with > an understood latency hit resulting from purely synchronous writes. > > The part I'm unsure about is how the RADOS GW fits into this picture. > For high availability (and to improve best-case latency on reads), > we'd want to run a gateway in each data centre. However, the first > paragraph of the following post suggests this is not possible: > > http://article.gmane.org/gmane.comp.file-systems.ceph.devel/12238 > > Is there a hard restriction on how many radosgw instances can run > across the cluster, or is the point of the above post more about a > performance hit? It's talking about the performance hit. Most people can't afford data-center level connectivity between two different buildings. ;) If you did have a Ceph cluster split across two DC (with the bandwidth to support them) this will work fine. There aren't any strict limits on the number of gateways you stick on a cluster, just the scaling costs associated with cache invalidation notifications. > It seems to me it should be possible to run more > than one radosgw, particularly if each instance communicates with a > local OSD which can proxy reads/writes to the primary (which may or > may not be DC-local). They aren't going to do this, though — each gateway will communicate with the primaries directly. -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
