On Thu, 18 Jun 2009 14:51:32 +0200, Giuseppe Fuggiano <giuseppe.fuggiano@xxxxxxxxx> wrote: > 2009/6/18 Gordan Bobic <gordan@xxxxxxxxxx>: >> On Thu, 18 Jun 2009 17:11:42 +0530, Brahadambal Srinivasan >> <brahadambal@xxxxxxxxx> wrote: >>> Hi, >>> >>> I am trying to figure out if it is possible to create an RHCS cluster >> among >>> nodes that are in remote locations? If yes, then how are the following >>> handled? : >>> >>> 1. Storage - how is the shared storage acheived? >> >> Same as it is achieved locally. It is up to your SAN to handle this in a >> real-time, consistent way. You may want to look into DRBD >> (http://www.drbd.org) for the block device level replication. Be aware, >> however, that performance on the disk access front will be terrible, >> because the latency will end up being limited by your ping time on the >> WAN. >> So instead of it having 0.1ms added via a local gigabit interconnect, >> it'll >> have 50-100ms added to it. Most applications will not produce usable >> performance with this kind of disk I/O speed. > > I am wondering if that will affect both read and write requests or > only write/verify ones (which DRBD have to replicate using the > network). It'll affect both a lot of the time even if one site is passive/failover, and pretty much all the time if it's an active-active configuration with both sides handling load. DLM will end up bouncing and checking locks back and forth between the sites. This will be the case with any real-time distributed storage system that guarantees full consistency. In other words, load sharing over a WAN will have unusable performance in most cases. Within the same campus, it'd be OK, but between different continents, I don't see it being viable. The real question is whether you really need/want load sharing. If not, you can just use ext3 with DRBD in active-passive mode with failover. Or you can use a more farm-like approach where the servers are mostly serving data, and updates/writes can be streamed from a single master using something like SeznamFS. Gordan -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
