We have the following stats on single node cassandra on Amazon EC2/Rightscale m1.large instance with 2 ephemeral disks with raid0. (7.6 GB Total Memory)
4 GB RAM is allocated to cassandra Heap, 800MB is Heap NEW size.
following stats are from OpsCenter community 2.0
Read Requests 285 to 340 per second
Write Requests 257 to 720 per second
OS Load 15.15 to 17.15
Write Request Latency 293 to 685 micros
OS Sent Network Traffic 18 MB to 30 MB per second
OS Recieved Network Traffic 22 MB to 34 MB per second
OS Disk Queue Size 23 to 26 requests
Read Requests Pending 8 to 20
Read Request Latency 69140 to 92885 micros
OS Disk latency 37 to 42 ms
OS Disk Throughput 12 to 14 Mb per second
Disk IOPs Reads 600 to 740 per second
Disk IOPs Writes 2 to 7 per second
IOWait 60 to 70 % CPU avg
Idle 24 to 30 % CPU avg
Rowcache is disabled.
Are the above stats are satisfying with the provided configuration....OR how could we tweak it more to get less IOWait..........because we think that we are experiencing lots of IOWait.....how could we tweak it to get the best.
Read Requests are mixed.........some are from one super column family and one standard having more than million keys......and varying no. of super columns max 14 with varying no. of subcolumns from 1 to 10000 and varying no. of columns max 14 in standard column family...............subcolumns are very thin in nature with 0 bytes value....8 bytes for name.
Process is removing the data from super column family and writing the processed data on standard one.
Would EBS Disks work better....on Amazon EC2
I'm not positive whether you can tweak your config easily to get more disk performance, but using Snappy compression could help a good deal in making your app need to read less overall. It may also help to use the new composite key layout instead of supercolumns.
One thing I can say for sure: EBS will NOT work better. Stay away from that at all costs if you care about latency.