Disk I/O scheduling

asked 2017-04-12 03:35:29 -0500

SamHill gravatar image

I am currently in the process of testing an installation of Vertica to an Openstack deployment.

Vertica requires setting the disk scheduler for any node to either deadline or noop however modifying both the settings in the bootloader or /sys/block/{device}/queue/scheduler has no effect.

Is there a way of changing this or would i have to change something in the default nova settings ?

And does changing the schedule type for Openstack disks have any meaningful effect on performance?

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Nova doesn't care for settings inside the virtual machine; it doesn't interfere with the VM's storage scheduler parameters. On the other hand, what looks like a disk to the VM may be a file on the VM host, so that settings that are optimal for a physical server could be bad for a VM.

Bernd Bausch gravatar imageBernd Bausch ( 2017-04-12 18:37:44 -0500 )edit

How do you know that changing the settings has no effect? Does Vertica complain?

Bernd Bausch gravatar imageBernd Bausch ( 2017-04-12 18:38:30 -0500 )edit

If I echo Deadline or Noop into /sys/block/{device}/queue/scheduler the change doesn't save. It just stays at none. Same with changing the value in the grub config.

The Vertica installation script queries quite a few things such as diskreadahead , io scheduling etc before it installs.

SamHill gravatar imageSamHill ( 2017-04-13 06:02:48 -0500 )edit

You can override these warning if you need to but I was under the impression in virtualised environments hyperv/vmware etc setting the disk scheduler for a guest vm to NOOP/Deadline was considered a good idea to maximise performance.

SamHill gravatar imageSamHill ( 2017-04-13 06:02:53 -0500 )edit

Does Openstack treat its virtual disks in a significantly different way to other virtualisation solutions?

SamHill gravatar imageSamHill ( 2017-04-13 06:02:57 -0500 )edit