Input/output threads (I/O threads) are dedicated event loop threads for supported disk devices. I/O threads perform block I/O requests that can improve the scalability of some systems, in particular Symmetric Multiprocessing (SMP) host and guest systems that have many logical unit numbers (LUNs).

We recommend pinning I/O threads to physical CPUs that reside in the same non-uniform memory access (NUMA) node. This sample XML configuration defines four I/O threads for the disk devices by using the iothreads XML element, and pins CPUs 4, 6, 8, and 10 to I/O threads 1, 2, and 3 by using the iothreadpin XML element.