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Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm

From: Christian Brunner
Subject: Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm
Date: Fri, 21 May 2010 00:16:46 +0200

2010/5/20 Anthony Liguori <address@hidden>:
>> With new approaches like Sheepdog or Ceph, things are getting a lot
>> cheaper and you can scale your system without disrupting your service.
>> The concepts are quite similar to what Amazon is doing in their EC2
>> environment, but they certainly won't publish it as OpenSource anytime
>> soon.
>> Both projects have advantages and disadvantages. Ceph is a bit more
>> universal as it implements a whole filesystem. Sheepdog is more
>> feature complete in regards of managing images (e.g. snapshots). Both
>> projects require some additional work to become stable, but they are
>> on a good way.
>> I would really like to see both drivers in the qemu tree, as they are
>> the key to a design shift in how storage in the datacenter is being
>> built.
> I'd be more interested in enabling people to build these types of storage
> systems without touching qemu.

You could do this by using Yehuda's rbd kernel driver, but I think
that it would be better to avoid this additional layer.

> Both sheepdog and ceph ultimately transmit I/O over a socket to a central
> daemon, right?  So could we not standardize a protocol for this that both
> sheepdog and ceph could implement?

There is no central daemon. The concept is that they talk to many
storage nodes at the same time. Data is distributed and replicated
over many nodes in the network. The mechanism to do this is quite
complex. I don't know about sheepdog, but in Ceph this is called RADOS
(reliable autonomic distributed object store). Sheepdog and Ceph may
look similar, but this is where they act different. I don't think that
it would be possible to implement a common protocol.


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