[Sheepdog] questions from a newbie

Wenhao Xu xuwenhao2008 at gmail.com
Wed Sep 21 19:26:39 CEST 2011

On Tue, Sep 20, 2011 at 2:08 AM, MORITA Kazutaka <
morita.kazutaka at lab.ntt.co.jp> wrote:

> At Mon, 19 Sep 2011 16:45:06 -0700,
> Wenhao Xu wrote:
> Hi Wenhao,
> Thanks for your interest!
> >
> > Hi folks,
> >
> > I just started looking at the sheepdog project. I really like what you
> are
> > doing here and would like to contribute code in the near future. After
> > reading the slides from kvm forum, I have the following questions:
> > 1. How to determine the id for an object? E.g. for a data object inside a
> > VDI, how to give it an ID?
> The object ID is a 64 bit integer.  The upper 32 bit is a vdi ID,
> which is calculated from a vdi name with a hash function.  The lower
> 32 bit is an index of the data object.  Sheepdog splits a virtual disk
> into 4 MB chunks (data objects), and the index is used for the lower
> 32 bit.
> > 2. What is the relationship between vdi object and inode? How to locate
> > them? Are they also located by using consistency hashing?
> Both are same.  We should unify the names.  Vdi objects are also
> located with consistent hashing.
> > 3. Can each vdi volume have its own replication factor?
> Currently no, but it should have.
> > 4. How is the user_xattr is used? Why it is required by sheepdog?
> It is used to store some cluster informations (e.g. the creation time
> of cluster).  If possible, I'd like to remove the dependency.
> > 5. Corosync uses multicast to do communications. However, in data center,
> > multicast may be disabled on the switch/router. Is it easy to replace
> > corosync with another engine to manage the node membership, e.g.
> zookeeper?
> > I would be very happy to contribute on this part.
> I think it is not so difficult.  We have a plan to introduce a cluster
> driver which abstracts cluster management, and move all corosync
> related codes to the driver.  I think we can support zookeeper in the
> driver.
> This sounds great. Is the cluster driver interface available now? Having a
concept of cluster driver really helps.

> Currently, my coworker is working on a new cordination system project
> to become an alternative of corosync in Sheepdog.  I guess he can
> announce the project soon.
Great. Looking forward to hear more about it.

> Thanks,
> Kazutaka

Thanks for the reply, Kazutaka.


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