Limit dd speed on busy systems when copying or LVM volumes or backuping VMs

Submitted by mcordas on Thu, 01/06/2011 - 08:53 Pro Licensee

Here's the problem :

We have a busy KVM host. Sometimes, we need to make a copy or to clone a VM. Or we schedule a weekly backup of our VMs.

When that happens, iowait jumps, the host gets busy and the other VMs start suffering too for 10 or 15 minutes. Not too good for websites responsiveness.

Would it be possible to choose wether or not to limit dd speed, using for exemple "cpipe -s " ? Copying a volume would take longer, but dd would leave io ressources for other processes.

Thanks in advance,

Regards.

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Comments

Submitted by JamieCameron on Thu, 01/06/2011 - 12:32

There is actually a way to do this in Cloudmin already, using IO priorities. If you go to Cloudmin Settings -> Cloudmin Configuration -> Backup options, you can set an IO class that will be used for all tar and dd commands. I'd recommend "idle" , as that is lower than the default of "best effort".

Let us know if that helps ..

Submitted by mcordas on Thu, 01/06/2011 - 17:10 Pro Licensee

OK, thanks, we'll give a try. And what does "Linux IO scheduling priority" do ?

Submitted by JamieCameron on Thu, 01/06/2011 - 18:39

That also adjusts the IO priority, within the same class. See the ionice man page for the full details ..