Troubleshooting High I/O Wait in Linux. Linux has many tools available for troubleshooting some are easy to use, some are more advanced. I/O Wait is an issue that requires use of some of the more advanced tools as well as an advanced usage of some of the basic tools. The reason I/O Wait is difficult to troubleshoot is due to the fact that by default there are plenty of tools to tell you that your system is I/O bound, but not as many that can narrow the problem to a specific process or processes. Answering whether or not I/O is causing system slowness To identify whether I/O is causing system slowness you can use several commands but the easiest is the unix command top. # top top - 14:31:20 up 35 min, 4 users, load average: 2.25, 1.74, 1.68 Tasks: 71 total, 1 running, 70 sleeping, 0 stopped, 0 zombie Cpu(s): 2.3%us, 1.7%sy, 0.0%ni, 0.0%id, 96.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 245440k total, 241004k used, 4436k free, 496k buffers Swap: 409596k total, 5436k used, 404160k free, 182812k cached Finding which disk is being written to.
Detecting Disk I/O-bound Applications in Server Systems. In my previous blog, “Detecting CPU-bound Applications in Server Systems”, I discussed how to detect a CPU-bound application. I continue the performance analysis and debugging discussion here in my second blog called “Detecting Disk I/O Bound Applications in Server Systems”. Here I will show what common Linux* utilities can be used to detect I/O bound applications, and then I will cover what technologies are available to increase overall I/O performance of servers. Analyzing Linux* servers for I/O bound applications I conduct this test on a machine running Red Hat Enterprise Linux* 6.3, but you should be able to download all the utilities mentioned even if you work with other Linux* distributions.
When intensive disk I/O applications run, they may consume almost all available disk I/O resources, which may result in other disk I/O dependent applications contending for this resource. Therefore intensive disk I/O applications can slow down the whole system. #vmstat 5 #iotop /dev/sdb: /dev/sda: Determining Specific File Responsible for High I/O. Linux Wait IO Problem.
Wait IO problem can be caused by several reasons, the basic road-map to find out is which process is "eating" your CPU first and then determine why. The main cause are those background processes with "D" status code which means "Uninterruptiable sleep". But the those processes with "D+" which means "Uninterruptible sleep foreground process" will generally not cause the serious problem as those background processes. In this example, the cause of Wait IO is the File System Journal, so the configuration of file system is the cause of the problem. By Quentin Sherman Xue - CEO Looking for a Switch that can switch ISO 8583 transactions? Take a look on our EMB Switch Detection of Problem When you log into a Linux box, if the WA is present and with very high percentage, you will feel the login process will take much longer time than the normal. Determination of Problem The vmstat command shows you both foreground and background processes.
The Cause Solution Questions, feedback, suggestions? IO Wait causing so much slowdown (EXT4 JDB2 at 99% IO ) During Mysql Commit. Pinpointing I/O bottlenecks on Linux | Dirty Cache. Does this story sound familiar? The end users of a database application start complaining about poor system response and long running batch jobs. The DBA team starts investigating the problem. DBA’s look at their database tools such as Enterprise Manager, Automatic Workload Repository (AWR) reports, etc. They find that storage I/O response times are too high (such as an average of 50 milliseconds or more) and involve the storage team to resolve it. The storage guys, in turn, look at their tooling – in case of EMC this could be Navisphere Analyzer, Symmetrix Performance Analyzer (SPA) or similar tools. They find completely normal response times – less than 10 milliseconds average. The users still complain but the storage and database administrators point to each other to resolve the problem.
So what could be the issue here? Performance troubleshooting is a complex task and really there could be all kinds of reasons why this situation happens. Iostat -xk <interval><disks> Like this: Related. Iotop's homepage. Understanding Disk I/O - when should you be worried? Our co-author today is Christian Paredes, Senior System Administrator at Blue Box Group, a Ruby on Rails-focused web host that specializes in providing the operations expertise required to keep powerful apps running at peak performance. Christian keeps Blue Box Group’s internal infrastructure in top-shape and provides tier 3 customer support. He also volunteers for LOPSA, a guild for system administrators. We’re pleased to have him share some of his expertise on disk I/O. If you’re old enough to remember floppy drives, you’ve heard the symptoms of a disk I/O bottleneck. For example, while Oregon Trail loaded the next scene, you’d hear the drive grinding away, reading data from the disk.
It’s more difficult to detect an I/O bottleneck if the disk isn’t on your desktop. Do you have an I/O bottleneck? A banana slug vs. an F-18 Hornet Disk I/O encompasses the input/output operations on a physical disk. The killer when working with a disk? Do you have an I/O bottleneck? Three takeaways.