Re: [Qemu-devel] Re: [ANNOUNCE] Sheepdog: Distributed Storage System for KVM

[MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>]

On Fri, Oct 23, 2009 at 8:10 PM, Alexander Graf <agraf@suse.de> wrote:
>
> On 23.10.2009, at 12:41, MORITA Kazutaka wrote:
>
> On Fri, Oct 23, 2009 at 12:30 AM, Avi Kivity <avi@redhat.com> wrote:
>
> How is load balancing implemented?  Can you move an image transparently
>
> while a guest is running?  Will an image be moved closer to its guest?
>
> Sheepdog uses consistent hashing to decide where objects store; I/O
> load is balanced across the nodes. When a new node is added or the
> existing node is removed, the hash table changes and the data
> automatically and transparently are moved over nodes.
>
> We plan to implement a mechanism to distribute the data not randomly
> but intelligently; we could use machine load, the locations of VMs, etc.
>
> What exactly does balanced mean? Can it cope with individual nodes having
> more disk space than others?

I mean objects are uniformly distributed over the nodes by the hash function.
Distribution using free disk space information is one of TODOs.

> Do you support multiple guests accessing the same image?
>
> A VM image can be attached to any VMs but one VM at a time; multiple
> running VMs cannot access to the same VM image.
>
> What about read-only access? Imagine you'd have 5 kvm instances each
> accessing it using -snapshot.

By creating new clone images from existing snapshot image, you can do
the similar thing.
Sheepdog can create cloning image instantly.

-- 
MORITA, Kazutaka

NTT Cyber Space Labs
OSS Computing Project
Kernel Group
E-mail: morita.kazutaka@lab.ntt.co.jp