I had some disk io issues recently with NFS, I found the command 'iostat -x 5' to be a great help when using Linux.

For example here is the output when I do a 10GB file transfer onto hdc
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util hdc 0.00 875.95 0.00 29.66 0.00 7244.89 0.00 3622.44 244.27 3.07 103.52 1.78 5.27

The last field show the disk is 5.27% busy.

I have seen this value at 100%, adding more server brought it under 100%.
It seems that if you hit 100% problems sort of cascade all over that place. For example Apache connections went right up and hit their max.

I am not sure how accurate the % is but it has work pretty well for me.

Perhaps use this command in another window with you run your SQL and see what it shows.

Kind regards,

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