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i have question about waiting for HDD. I'm not sure what is optimal %wa.

Server running browser game, i know that there is a lot hdd writing but im not sure what is optimal %wa. Server running 8 cores processor with 16gb of RAM. Mysql uses 20-35% CPU, and running 3 MySql databases.

%wa is 5-15% when 150 players are online. Is that ok or i didn't configured mysql, php or something other ok?

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possible duplicate of Can anyone explain precisely what IOWait is? –  Michael Hampton Mar 5 '13 at 11:25
    
I know what IOWait is. I am asking about optimal values for waiting for HDD %wa. I had problems with HDD and hosters change it. new one works fine and today starts to have again 5-10% of %wa and php calculation is slower. –  EmptySD Mar 5 '13 at 14:38
    
Problem is solved by changing innodb_buffer_pool_size. After i changed from 8MB to 1Gb mysql used a lot more RAM and entire problem with %WA is fixed (now is 0.8-1.2 all the time). Also server finally works perfect. –  EmptySD May 7 '13 at 8:12
    
I'm glad to hear you fixed your underlying problem. But that has absolutely nothing to do with the question you asked here, and you never even told us anything that might have let us help with that issue. –  Michael Hampton May 7 '13 at 16:21
    
Yes sorry, you are right, i didn't know that there is any problem with MySLQ configuration. I was running default MySQL config and looks that they are not good for mine needs. After i change that, mysqld process use more CPU% (sometimes 100%-150%) but there is no problems with MySQL waiting for write. –  EmptySD May 8 '13 at 19:36
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1 Answer

Optimal wait is 1%. What Michael wanted to point out is that if you want to lower IO-wait, you have to optimize your disk-throughput.

From experience I can say that a system is still quite reactive with about 20% IO-wait.

You should propably change the focus of your question to "how do I optimize disk-IO".

In that case you have to provide more detailed data from iostat -d 5, iostat -dm 5 and about your setup. From what you wrote the write-requests seem to be the most problematic.

So enabling a write-chache or putting that write-area into a ram-disk may change - but that is just a shot into the blue from my side.

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Problem is solved by changing innodb_buffer_pool_size. After i changed from 8MB to 1Gb mysql used a lot more RAM and entire problem with %WA is fixed (now is 0.8-1.2 all the time). Also server finally works perfect. –  EmptySD May 7 '13 at 8:11
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