Touretsky, Gregory wrote:
Hi,Does anyone have an experience running HDFS cluster stretched over high-latency WAN connections? Any specific concerns/options/recommendations? I'm trying to setup the HDFS cluster with the nodes located in the US, Israel and India - considering it as a potential solution for cross-site data sharing...
I would back up todd here and say "don't do it -yet". I think there are some minor placeholders in the rack hierarchy to have an explicit notion of different sites, but nobody has done the work yet. Cross datacentre data balancing and work scheduling is complex, and all the code in Hadoop, zookeeper, etc, is built on the assumption that latency is low, all machines clocks are going forward at roughly the same rate, the network is fairly reliable, routers are unlikely to corrupt data, etc.
Now, if you do want to do >1 site, it would be a profound and useful development -I'd expect the MR scheduler, or even the Pig/Hive code generators , to take datacentre locality into account, doing as much work per site as possible. The problem of block distribution changes too, as you would want 1 copy of each block in the other datacentre. Even then, I'd start with sites in a single city, on a MAE or other link where bandwidth matters less. Note that (as discussed below) on the MAN scale things can start to go wrong in ways that are unlikely in a datacentre, and its those failures that will burn you
worth reading http://status.aws.amazon.com/s3-20080720.html http://www.allthingsdistributed.com/2008/12/eventually_consistent.html -Steve
