virt January 2013

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create a guest
by mattias 16 Jan '13

16 Jan '13

can i create a guest with libvirt and use an existing disc with freebsd?

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xen device mapping/translation
by Luis Fernando Alen 16 Jan '13

16 Jan '13

Hello, list. Yesterday I was pleased to see that Centos has released official images at the aws marketplace. Nice job. Today I started playing with the Centos 6.3 image ( https://aws.amazon.com/marketplace/pp/B00A6L6F9I, on which I plan to deploy a gluster cluster in production soon) and noticed a weird thing. EBS Volumes attached to sd<X> are translated to xvd<Y> at the OS level. However, after a few research and IRC chat, I figured out that it's not weird, it's actually a normal and expected behavior (thanks for your help, z00dax). sdX is actually mapped to xvdX+4. There is a consistent offset of 4. Suppose you attach an ebs volume to /dev/sdf. It'll be translated to xvdj at the OS level. sdg to xvdk, sdh to xvdl and so on. Allright. After having figured the mystery out, it became easy to work on automations that deal with ebs volumes and file systems, such as volumes created, attached and mounted on the fly, snapshots that freeze file systems and so on... However, I really do think to myself: Wouldn't it be cleaner if the image use simple translation (sdX to xvdX)? If I'm not wrong, Rightscale uses this on their Centos images and it's much simpler. There's no extra work needed to deal with that 4 offset when you want to automate things. Is there a reasonable reason for the 4 offset which makes it unchangeable? It's just a thought. I think it's worth considering it.. Luis Alen www.izap.com.br Ligue com tarifa local de todo o Brasil 4020.3000

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kvm
by mattias 16 Jan '13

16 Jan '13

i have installed kvm on centos 6 but how to run it i not use libvirt

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Best practices on KVM systems
by Luca Gervasi 12 Jan '13

12 Jan '13

Hello, i'm trying to create some best practices on my centos 6.3 / libvirt /kvm hypervisors. Actually, i use NFS as shared storage backend for every VM and make reasonable use of the KSM (enabling it into qemu.conf). Every VM is configured with VirtIO drivers (when possible) and the disks use none as cacheing method to allow me live migration. I'll be happy to know if there are some more improvements i can implement. Please share your knowledge. Thanks in advance Luca Gervasi

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Andreas Reschke is out of the office
by Andreas Reschke 11 Jan '13

11 Jan '13

Ich werde ab 11.01.2013 nicht im Büro sein. Ich kehre zurück am 21.01.2013.

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mirroring people.centos.org
by Carl T. Miller 07 Jan '13

07 Jan '13

Is there an easy way to mirror people.centos.org? I tried "rsync people.centos.org::" and it gives some disclaimers followed by a null list of available modules. I've got an ugly workaround using wget, but would prefer to use rsync. c -- Carl T. Miller Systems Engineer carl(a)carltm.com

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CentOS AWS AMIs?
by Richard Clark 07 Jan '13

07 Jan '13

Hi list, I've noticed that instance-backed AMIs no longer seem to exist for the 'official' CentOS images, though the EBS ones are fine.. Looking at the wiki (http://wiki.centos.org/Cloud/AWS), the AMIs listed on marketplace are slightly newer than what's listed on the wiki, so just wondering if something got overlooked after the last build? Cheers, -- Richard Clark richard(a)fohnet.co.uk

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Download official CentOS AMI?
by Karl Ward 07 Jan '13

07 Jan '13

I'd like to download the official CentOS AMI files for 6.3 x86_64, but that does not seem possible. The goal is to use the same image on both public and private clouds, to improve consistency. Are the AMI files available for download anywhere, or from anyone? I offer my apologies if the CentOS-virt list is not the correct contact for this query. -- Karl Ward

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Re: [CentOS-virt] Time
by James B. Byrne 02 Jan '13

02 Jan '13

On Wed, January 2, 2013 03:53, Robert Dinse wrote: > > Friday, I moved our servers to a new co-lo facility and ran into > an interesting problem with virtual machines. > > I did an orderly shutdown of the CentOS 6.3 host, and it in > turn suspends all the guests. It took about an hour and a half > to move and fire up the host. > > The guests, being suspended, were then an hour and a half > behind and it seems ntpd does not want to correct more than 1000 > seconds of error so it would not automatically adjust the clocks. > > I tried the -g argument which is supposed to override the > 1000 second limit but it did not. I ended up having to manually > set the clocks close enough for ntpd to correct. > > Since there is no hardware clock for the virtual machines > to use when they boot, it seems that shutdown and reboot of the > virtual machines probably would not have avoided this. > > Any suggestions for addressing this particular scenerio other > than having to manually set a bunch of clocks? > I ran into this situation several times whilst testing KVM and the lessons I learned from the experiences can be summarized as: 1. Never allow the kvm hypervisior to handle guests during a host shutdown. Use 'virsh shutdown' on each of the guests first and then shutdown the host. Use autostart to restart guests on a host's reboot. Write a script to process 'virsh list' to feed active domains to 'virsh shutdown' if automation is required and link that to /etc/rc0.d/K10<whatever>. 2. In the situation where a kvm guest pause and restore sequence leads to an excessive disconnect between guest time and wall time use ntpd -q to hard set the time. From the guest's point of view you are always going ahead in time in the case of a pause and resume so this is not likely to ever cause a problem. But, having written that down, it probably will at some point. 3. Run ntpd on the host system and have its guests configured to only use that time server source. 4. On each guest have a cron job that checks for ntpd at regular intervals which reports failures and restarts the time service as necessary. We use: JOBNAME="Check ntpd status and restart if required" ; \ ntpstat > /dev/null && \ if [[ $? -gt 0 ]]; then /sbin/service ntpd start; fi -- *** E-Mail is NOT a SECURE channel *** James B. Byrne mailto:ByrneJB@Harte-Lyne.ca Harte & Lyne Limited http://www.harte-lyne.ca 9 Brockley Drive vox: +1 905 561 1241 Hamilton, Ontario fax: +1 905 561 0757 Canada L8E 3C3

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virt January 2013