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

From: MORITA Kazutaka
Subject: Re: [Qemu-devel] Re: [ANNOUNCE] Sheepdog: Distributed Storage System for KVM
Date: Sat, 24 Oct 2009 01:17:12 +0900

On Fri, Oct 23, 2009 at 8:10 PM, Alexander Graf <address@hidden> wrote:
> On 23.10.2009, at 12:41, MORITA Kazutaka wrote:
> On Fri, Oct 23, 2009 at 12:30 AM, Avi Kivity <address@hidden> 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
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