We use C* on m1.xLarge AWS EC2 servers, with 4 disks xvdb, xvdc, xvdd, xvde parts of a logical Raid0 (md0).

I use to see their use increasing in the same way. This morning there was a normal minor compaction followed by messages dropped on one node (out of 12).

Looking closely at this node I saw the following:


On this node, one of the four disks (xvdd) started working hardly while other worked less intensively.

This is quite weird since I always saw this 4 disks being used the exact same way at every moment (as you can see on 5 other nodes or when the node ".239" come back to normal).

Any idea on what happened and on how it can be avoided ?