6.2. I/O Scheduling with Red Hat Enterprise Linux as a Virtualization Guest
- Red Hat Enterprise Linux guests often benefit greatly from using the
noopscheduler. The scheduler merges small requests from the guest operating system into larger requests before sending the I/O to the hypervisor. This enables the hypervisor to process the I/O requests more efficiently, which can significantly improve the guest's I/O performance.
- Depending on the workload I/O and how storage devices are attached, schedulers like
deadlinecan be more beneficial than
noop. Red Hat recommends performance testing to verify which scheduler offers the best performance impact.
- Guests that use storage accessed by iSCSI, SR-IOV, or physical device passthrough should not use the
noopscheduler. These methods do not allow the host to optimize I/O requests to the underlying physical device.
6.2.1. Configuring the I/O Scheduler for Red Hat Enterprise Linux 7
deadline. However, on a Red Hat Enterprise Linux 7 guest machine, it may be beneficial to change the scheduler to
noop, by doing the following:
- In the
/etc/default/grubfile, change the
elevator=deadlinestring on the
elevator=noop. If there is no
elevator=noopat the end of the line.The following shows the
/etc/default/grubfile after a successful change.
cat /etc/default/grub[...] GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=vg00/lvroot rhgb quiet elevator=noop" [...]
- Rebuild the
- On a BIOS-based machine:
grub2-mkconfig -o /boot/grub2/grub.cfg
- On an UEFI-based machine:
grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg