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From Francois Richard <>
Subject RE: do I need to add more nodes? minor compaction eat all IO
Date Sat, 23 Jul 2011 21:16:37 GMT
This really depends on your disks setup.

When you run iostat under high load, do you see a high number of r/s but the rMB/s is not
so great?

I usually use:

iostat -x -m sdb sdc 1 to monitor situation like this.

In my case my disk setup is the following:

OS --> /sda
Cassandra CommitLogs --> /sdb
Cassandra Data --> /sdc

My understanding is that during compaction cassandra does a lot of non sequential readsa then
dumps the results with a big sequential write.

Is your application mostly doing writes and little reads or the other way around.


-----Original Message-----
From: Yan Chunlu [] 
Sent: Saturday, July 23, 2011 9:16 AM
Subject: do I need to add more nodes? minor compaction eat all IO

I have three nodes and RF=3, every time it is do minor compaction, the cpu load(8 core) get
to >30, and iostat -x 2 shows utils is 100%, is that means I need more nodes?  the total
data size is <60G



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