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Matt
Asked: 2011-05-08 04:11:07 +0800 CST

Linux-KVM and Ganeti - help me understand / deploy

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Looking to build a small (but future proof) Linux-KVM cluster with Ganeti

I'm starting my setup with 2 HVM machines, each with 2x 500GB SATA disk.

I've studied the documentation and I have a fair understanding of the system. However certain things are still unclear and I am unable to find straight answers. I'm hoping a more seasoned user can share some insight on these:

1. Should I use software RAID1 (mirror) on the physical machines?

My machines currently do not have hardware RAID controllers. Ganeti states that 'DRBD is RAID1 over network'. Somewhere claimed the old docs advised against using software raid, but I can not confirm this.

2. Grasping fail-over/mirror scenarios in the cluster ?

If I understand the limitations of DRBD correctly you can only sync to 1 other node. So in my scenario I'd use:

  • [box1] master & node
  • [box2] master-candidate & node

after boxN crashes I can deploy the other box and hopefully fix/rebuild the crashed box through standard Ganeti commands. If I add a box3 to the cluster - what can I do with it DRBD-wise? Is it like a hot-spare that should be deployed to restore another completely failed box? I'm not understanding the principle here.

3. Can I run *BSD instances ?

I'm able to run *BSD virtual machines on Linux-KVM, however Ganeti seems to be Linux-instance-only? I've seen the Ganeti instance manager which mentions FreeBSD in the issue queue but I'm unsure if I will be able to deploy *BSD instances through Ganeti? It's okay if manual work is involved setting them up, but I'm unsure I can use all of Ganeti's features on such an instance once it has been setup.

4. Out-of-band management for 'customers' ?

I've seen the VNC options and serial console options but since Ganeti claims to be 'intrusive on the host as it takes over SSH key management' I'm wondering if I can provide out-of-band commandline management to other users alongside it (ssh with fixed command for specific instance stop/start etc). Or does Ganeti provide something like that for 'single-instance-owners'?

virtualization kvm-virtualization cluster ganeti

1 Answers

  1. Best Answer

    To answer my own questions; perhaps of use to someone:

    1. yes, if you can using software raid is better than no software raid
    2. an instance (virtual guest) is hosted on nodeA while DRBD mirrors the instance's disk on nodeB. If nodeA fails you can 'move' the instance to the backup nodeB. This is a manual process and not fully automated. You can also move nodes around for other reasons (performance etc)
    3. Yes. Automated installation of instances is a DIY scripting thing though.
    4. Yes you can.
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