"(I originally saw 3-5 ms read latency with a small amount of data and 1 Keyspace/CF)? "
The 3~5ms latency is offered by the Filesystem page cache. Because your dataset is small, it can be cached totally by Filesystm. 2010/5/11 Peter Schüller <sc...@spotify.com> > > isolated requests, obviously in scale the RAID should perform better... I > > have not started testing concurrent reads in scale as the single reads > are > > too slow to begin with. I am getting 20-30ms response time off of > internal > > Concurrent reads is what you need to do in order to see the benefit of > a RAID controller with many constituent drives under it. > > > drives and 50-70 ms response time through the raid volumes (as reported > in > > cfstats). The system is totally idle and all data has been cleanly > > That said, a RAID controller imposing several tens of extra > milliseconds of latency sounds strange; something else or fishy has to > be going on. > > But don't expect sequential reads of non-cached small random-access > data to be faster with a RAID controller. The benefit of RAID will > tend to be overall throughput when doing concurrent reads, fast > fsync() (low latency on durable writes) and the ability to eat bursts > of write activity in battery backed cache. > > -- > / Peter Schuller aka scode >
