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I have number of MySQL databases, I have used tools such as dstat, vmstat I'm just unable to determine when do I need to add more drives to increase performance.

the number of databases are increasiing over months and I have been asked to increase the performance, I have been adding faster drives, but I would like to know if there is an easy way to know if the system for example the number of iops being used is over %80 therefore you need to add more drives .. etc

Thank you

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What do those tools tell you in your analysis? –  ewwhite Jan 25 '13 at 17:32
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2 Answers

up vote 3 down vote accepted

iostat's TPS (Transactions Per Second) column will give you the IOPS per volume usage metrics that you need to make this analysis.

Once you have that, all you need to do is find your max IOPS by doing some basic math based on your current disk configuration, and you're good to go.

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I'm using 7.5K RPMs which comes with 75 iops, enterpise SATA 15K comes with 200 iops, can you give me an example? –  user1007727 Jan 25 '13 at 15:49
    
An example of what? If you want me to do your max IOPS calculation, you'll need to provide the estimated IOPS per disk (manufacturers publish this in the disk's whitepapers), what RAID level you have, how many spindles per RAID, and what % of your workload is read and what % is write. –  MDMarra Jan 25 '13 at 15:51
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More detail on your storage array hardware, please? Also, operating system/distribution version and kernel version.

RAW IOPS counts are abstracted by other factors. If using hardware RAID, the presence or lack of a battery-backed or flash-backed write cache is a HUGE factor in storage performance. That's the biggest influence, followed by number of disks, whether you have SSD drives available, etc.

You also need to know what your read/write patterns are.

Can you update your question with more information about the environment?

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