I was recently reading our documented Best Practices for running Linux on Hyper-V and noticed this section:
Use I/O scheduler NOOP for better disk I/O performance.
The Linux kernel has four different I/O schedulers to reorder requests with different algorithms. NOOP is a first-in first-out queue that passes the schedule decision to be made by the hypervisor. It is recommended to use NOOP as the scheduler when running Linux virtual machine on Hyper-V. To change the scheduler for a specific device, in the boot loader’s configuration (/etc/grub.conf, for example), add elevator=noop to the kernel parameters, and then restart.
This is interesting – as I often get asked by people about what they can do to ensure the best performance when running Linux on Hyper-V.
For a bit of background here – Linux utilizes a number of techniques to try and get the best performance out of your storage (you can read all about this if you do a search on “Linux IO elevator”). Unfortunately, all of this logic is completely undone inside of a virtual machine – as we are then responsible for mapping virtual storage to physical storage in a way that is hidden from the guest operating system. Turning effect of turning on the NOOP I/O scheduler is that Linux stops trying to be clever about storage activity – and instead relies on the underlying hardware (virtual hardware in this case) to do the right thing.
In our testing this has always yielded the best results.