Couple of hits here, one from jonathan and some previous discussions on the user list http://www.google.co.nz/search?q=cassandra+iostat

Same here for cfhistograms http://www.google.co.nz/search?q=cassandra+cfhistograms 
cfhistograms includes information on the number of sstables read during recent requests. As your initial cfstats showed 236 sstables I thought it may be useful see if there was a high number of sstables been accessed per read. 

70 requests per second is slow against a 6 node cluster where each node has 12 cores and 96GB of ram. Something is not right.

Aaron 
On 12 Apr 2011, at 17:11, mcasandra wrote:


aaron morton wrote:

You'll need to provide more information, from the TP stats the read stage
could not keep up. If the node is not CPU bound then it is probably IO
bound.


What sort of read?
How many columns was it asking for ?
How many columns do the rows have ?
Was the test asking for different rows ?
How many ops requests per second did it get up to?
What do the io stats look like ?
What does nodetool cfhistograms say ?

It's simple read of 1M rows with one column of avg size of 200K. Got around
70 req per sec.

Not sure how to intepret the iostats output with things happening async in
cassandra. Can you give little description on how to interpret it?

I have posted output of cfstats. Does cfhistograms provide better info?


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