


When encountering a disk IO bottleneck, you should first confirm the root cause of the problem and then optimize it. 1. Use iostat, iotop and other tools to confirm whether there are IO bottlenecks, pay attention to %util and await indicators; 2. Analyze application behavior, reduce small files reading and writing, enable file system cache, and optimize log writing methods; 3. Select a suitable file system such as ext4 or XFS to improve IO efficiency; 4. Adjust the IO scheduling strategy, choose noop or deadline in SSD, and use CFQ in mechanical hard disks; 5. Use cache (such as Redis) and asynchronous IO mechanism to reduce disk pressure.
When encountering a disk IO bottleneck, many people's first reaction is to upgrade their hardware, but in fact, many times the problem lies in configuration, usage or monitoring blind spots. To solve this kind of problem, the key is to figure out which link the bottleneck lies and then prescribe the right medicine.
Check system load and IO usage
First, we need to confirm whether there is really an IO bottleneck. Commonly used commands in Linux include iostat
, iotop
and vmstat
. These tools can help you see the current disk's read and write speed, waiting time, and which process is reading and writing in large quantities.
- iostat -x 1 can refresh the detailed statistics once a second, focusing on
%util
(device utilization) andawait
(average waiting time). If these two values ??are high for a long time, it means that the IO pressure is high. - iotop can intuitively see which processes are "crazy" reading and writing to disk.
If you find that the system responds slowly, but the CPU and memory are very free, you should even doubt whether the disk is dragging you down.
Analyze application behavior and file systems
Sometimes it’s not that the hardware is not working, but that there is a problem with the program itself. For example, frequent small file reading and writing, no cache mechanism, and excessive log writing, etc., will lead to increased IO pressure.
Common practices include:
- Check whether any programs are doing full disk scanning or frequent synchronization
- Confirm whether appropriate file system cache is enabled (such as Linux page cache)
- Whether asynchronous writing is enabled in the log system (such as rsyslog queue mode)
In addition, different file systems also have different IO processing efficiency. For example, ext4, XFS, and btrfs perform significantly differently in some scenarios, and choosing the right file system can also relieve stress.
Adjust IO scheduling policies and parameters
Linux provides several IO schedulers (CFQ, deadline, noop, etc.), and you can choose the most suitable one according to your storage type. For example, SSDs are usually more suitable for noop or deadline, while mechanical hard drives may be more suitable for CFQ.
You can view and modify it in the following ways:
cat /sys/block/sda/queue/scheduler echo deadline > /sys/block/sda/queue/scheduler
In addition, some kernel parameters can be adjusted to optimize IO behavior, such as increasing /proc/sys/vm/dirty_ratio
, allowing the system to flush data to disk more delays and reduce frequent IO.
Using cache and asynchronous IO mechanisms
Rational use of cache can greatly reduce disk pressure. For example, memory databases such as Redis and Memcached are suitable for cache hotspot data; the application layer can also add local cache logic to reduce the frequency of direct access to disk.
At the same time, use asynchronous IO operations as much as possible. Like Node.js' fs.promises module, Python's asyncio and aiofiles can all avoid blocking the main thread and improve overall throughput.
Some databases also support asynchronous disk flushing. For example, when MySQL's innodb_use_native_aio option is enabled, it can improve concurrent write performance.
Basically these ideas. Troubleshooting IO bottlenecks requires analysis in combination with monitoring, system configuration and application behavior, which is not complicated but is easy to ignore details.
The above is the detailed content of How to troubleshoot disk IO bottlenecks. For more information, please follow other related articles on the PHP Chinese website!

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