On Thu, Jan 20, 2011 at 2:13 PM, Mick Semb Wever <m...@apache.org> wrote: > To go with raid-5 disks our hosting provider requires proof that iSCSI > won't work. I tried various things (eg `nodetool cleanup` on 12Gb load > giving 5k IOPS) but iSCSI seems to keep up to the performance of the > local raid-5 disks... > > Should i be worried about using iSCSI?
It should work fine; the main reason to go with local storage is the huge cost advantage. Of course with a SAN you'd want RF=1 since it's replicating internally. > Are there better tests i should be running? I would test write scalability going from 1 machine, to half your planned cluster size, to your full cluster size, or as close as is feasible, using enough client machines running contrib/stress* (much faster than contrib/py_stress) that you saturate it. Writes should be CPU bound, so you expect those to scale roughly linearly as you add Cassandra nodes. Reads (once your data set can't be cached in RAM) will be i/o bound, so I imagine with a SAN you'll be able to max that out at some number of machines and adding more Cassandra nodes won't help. What that limit is depends on your SAN iops and how much of it is being consumed by other applications. *I just committed a README for contrib/stress to the 0.7 svn branch -- Jonathan Ellis Project Chair, Apache Cassandra co-founder of Riptano, the source for professional Cassandra support http://riptano.com
