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I want to know about how to view the disk I/O in linux so that i can check if i have to increase the ram.

Also the limits/thresholds after which i should increase the ram.

Thank You

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If you have kernel ≥ 2.6.20 with the TASK_DELAY_ACCT and TASK_IO_ACCOUNTING options enabled, i suggest iotop.

top like realtime display of system io. Great tool. iotop homepage

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Trending I/O can be done using something similar to iostat or sar (which is provided under the sysstat package under debian)

As to the limits/thresholds after which you should increase the amount of RAM it really depends on your machine and what you consider to be acceptable service levels.

Personally, I would be looking at the %iowait figure. Anything higher than about 5% is where you're likely to start seeing performance degradation.

From here you need to start looking at read/write trends. Keep in mind, if you're write bound then increasing the amount of RAM may NOT have any effect on performance.

HTH

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Try iostat. In Gentoo it's in app-admin/sysstat

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dstat -D total
iostat -d 2
vmstat -d 2
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if it's typical server case - install munin to see how load / io activity changes during the day / week. especially linux_diskstats_ is useful for analyzing your io bottlenecks.

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try iostat -dkx 2

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Ummm... you should use something like "free -m" to see how much RAM has been used. Once you start hitting swap space is when you should think about increasing it.

You can use "vmstat -n 2" to view disk I/O. For both commands have a read through the man pages to see how they work.

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