[sheepdog-users] 答复: Re: Re: re: Re: support for share storage

[Hitoshi Mitake]

At Wed, 3 Dec 2014 16:00:56 +0000,
Andrew J. Hobbs wrote:
> 
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> I think what you're missing is sheepdog does absolutely nothing in regard to shared locking, meta data, etc.  What you're looking for is more like GFS2 or OCFS running on your shared storage.  Or Ceph's MDS capabilities, although while they claim it works, it's still not recommended for production and there are performance issues with it.
> 
> What sheepdog will do is (as of 0.9) is provide a VDI level lock for the image such that only a single machine can access that VDI at a time.  Prior to that, if you accidentally started a VM on two different hosts, the images would corrupt as you had two simultaneously operating images in the same image with no protection.

Yes, sheepdog doesn't allow reading/writing from multiple clients at a
same time. As you say, it is completely meaningless. But once you
create iSCSI target based on sheepdog VDI, reading/writing from
multiple iSCSI initiators can be done correctly if the initiators do
locking by themselves. IIUC, GFS2 and OCFS have a capability of such
locking. So sheepdog + iSCSI + GFS2 or OCFS would work fine.

Thanks,
Hitoshi

> 
> 
> On 12/03/2014 03:40 AM, yang.bin18 at zte.com.cn<mailto:yang.bin18 at zte.com.cn> wrote:
> 
> >>     In this model,if node1 down,whether can /media/nas/node1 be loaded
> >> within other node online and guest can still access the data in
> >> /media/nas/node1 existed.
> 
> >The one you speak about is the standard share storage model.
> >Why don't you save your qcow2/raw files directly in the shared storage?
>        Because we have mutiple nodes to access the same shared storage the same time,so we need a clustered filesystem to manage.
> >Or export block devices by iscsi or nbd?
>        We use fiber storage.
> >In other words, that are the benefits of using sheepdog if you already
> >have a shared storage?
>        To implement concurrent access to the share storage from diffrecent nodes.
> 
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