Input/Output (I/O) scheduling is a crucial aspect of Linux systems, affecting how efficiently data is read from and written to storage devices. The I/O scheduler determines the order and priority of these operations, impacting system performance and responsiveness. This article will guide you on how to discover, configure, and optimize I/O schedulers in a Linux environment.

Understanding I/O Schedulers

Linux provides several I/O schedulers, each with its own algorithm and use case:

1. CFQ (Completely Fair Queuing): Distributes bandwidth equally among all processes.
2. Deadline: Prioritizes I/O requests to meet deadlines, reducing latency.
3. NOOP: Uses a simple FIFO (First In, First Out) queue, suitable for SSDs.
4. BFQ (Budget Fair Queuing): Focuses on providing predictable latency and high throughput.

Discovering Current I/O Scheduler

To find out which I/O scheduler your system is currently using, you can check the scheduler file for your storage device. Replace sda with your actual device identifier:

cat /sys/block/sda/queue/scheduler

This command will output something like:

noop deadline [cfq]

The scheduler in brackets is the one currently in use.

Changing the I/O Scheduler

To change the I/O scheduler temporarily, you can echo the desired scheduler into the scheduler file:

echo deadline | sudo tee /sys/block/sda/queue/scheduler

To make this change permanent, you need to edit your boot loader configuration. For systems using GRUB, follow these steps:

1. Edit the GRUB configuration file:

   sudo nano /etc/default/grub

2. Add or modify the line to include the desired scheduler. For example, to set the deadline scheduler:

   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash elevator=deadline"

3. Update GRUB:

   sudo update-grub

4. Reboot your system for the changes to take effect.

Practical Example

Let's say you want to switch to the NOOP scheduler for a device named sdb:

1. Check the current scheduler:

   cat /sys/block/sdb/queue/scheduler

2. Change to NOOP scheduler:

   echo noop | sudo tee /sys/block/sdb/queue/scheduler

3. Verify the change:

   cat /sys/block/sdb/queue/scheduler

Conclusion

Choosing the right I/O scheduler can significantly impact your system's performance, especially under heavy I/O loads. By understanding and configuring I/O schedulers, you can optimize your Linux system for specific workloads and hardware configurations.