[CentOS-virt] CentOS 6 kvm disk write performance
I have 2 similar servers. Since upgrading one from CentOS 5.5 to 6, disk write performance in kvm guest VMs is much worse. There are many, many posts about optimising kvm, many mentioning disk performance in CentOS 5 vs 6. I've tried various changes to speed up write performance, but northing's made a significant difference so far: - Install virtio disk drivers in guest - update the host software - Update RAID firmware to latest version - Switch the host disk scheduler to deadline - Increase host RAM from 8GB to 24GB - Increase guest RAM from 2GB to 4GB - Try different kvm cache options - Switch host from ext4 back to ext3 - Set noatime on the virtual disk image file Note: There is no encryption or on-access virus scanner on any host or guest. Below are some the block write figures in MB/s from bonnie++ with various configurations: First, figures for the hosts show that the CentOS 6 server is faster: 54CentOS 5 Host 50CentOS 5 Host 69CentOS 6 host 70CentOS 6 host Figures for a CentOS 6 guest running on the CentOS 5 host show that the performance hit is less than 50%: 30CentOS 6 guest on CentOS 5 host with no optimisations 27CentOS 6 guest on CentOS 5 host with no optimisations 32CentOS 6 guest on CentOS 5 host with no optimisations Here are the figures a CentOS 6 guest running on the CentOS 6 host with various optimisations. Even with these optimisations, performance doesn't come close to the un-optimised guest running on the CentoOS 5 host: 5 No optimisations (i.e. same configuration as on CentOS 5) 4 deadline scheduler 5 deadline scheduler 15 noatime,nodiratime 14 noatime,nodiratime 15 noatime 15 noatime + deadline scheduler 13 virtio 13 virtio 10 virtio + noatime 9 virtio + noatime The CentOS 6 server has a better RAID card, different disks and more RAM, which might account for the better CentOS 6 host performance. But why might the guest write performance be so much worse? Is this a known problem? If so, what's the cause?If not, is there a way to locate the problem rather than using trial and error? Thanks, Julian ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
[CentOS-virt] RAID: by host or within KVM?
Hi Virtualizers, I just setup a CentOS 6 box (at home) to run as a KVM host. It's replacing an absolutely ancient CentOS 5 server that's running Xen. I have one OS drive, and two drives in RAID 1 with LVM on top which is being used as the KVM storage pool. I created a KVM that will run OpenMediaVault (OMV). OMV requires an OS drive (which is really a LVM), and a separate drive(s) to put all the media on. This is where I'm a little unsure on how to proceed. I think I have two options: 1. Let the KVM host manage the drives (i.e. RAID with LVM on top) and just assign the single volume to OMV. OMV will see it as one HD. 2. Assign the individual drives to the OMV KVM, and let OMV manage the RAID creation, management, etc. I'm not sure which one will perform better. My hunch is if the RAID management is left at the host level, I'll see better overall performance. Performance isn't exactly my number one goal here, but I don't want to kill it completely either by going the wrong way. On the other hand, if I let OMV do the RAID management for the media storage disks, I'll gain future flexibility because it'll be much easier to move OMV to bare metal. Which way should I go? What would you guys do? Regards, Ranbir -- Kanwar Ranbir Sandhu ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
Re: [CentOS-virt] RAID: by host or within KVM?
I agree with Stephen. Option #1 is the way to go. On all of the KVM nodes I've personally built, I use a hardware RAID controller and let it manage the array. You could use software RAID on the host OS, but there are advantages of using hardware RAID (background array initialization, battery backed). Keep the RAID management at the hardware _or_ host OS (software raid) level and it will simplify administration. ---~~.~~--- Mike // SilverTip257 // On Fri, Aug 10, 2012 at 11:00 AM, Stephen Harris li...@spuddy.org wrote: On Fri, Aug 10, 2012 at 10:39:18AM -0400, Kanwar Ranbir Sandhu wrote: 1. Let the KVM host manage the drives (i.e. RAID with LVM on top) and just assign the single volume to OMV. OMV will see it as one HD. 2. Assign the individual drives to the OMV KVM, and let OMV manage the RAID creation, management, etc. I recommend option 1 simply because of recovery methodology. If you lose a disk and replace it, if the host controls the RAID then you have one point of repair and the VMs don't even notice. If, however, each VM does RAID itself then _each_ VM will need to perform disk replace and rebuild, which is a lot of admin overhead. Also that could cause a lot of disk contention and slow down the rebuild. Today you only have one VM. Tomorrow? :-) -- rgds Stephen ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
