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From Wido den Hollander <w...@widodh.nl>
Subject First review of RBD support for primary storage
Date Fri, 29 Jun 2012 15:59:34 GMT
Hi,

After a couple of months worth of work I'm happy to announce that the 
RBD support for primary storage in CloudStack seems to be reaching a 
point where it's good enough to be reviewed.

If you are planning to test RBD, please do read this e-mail carefully 
since there are still some catches.

Although the code inside CloudStack doesn't seem like a lot of code, I 
had to modify code outside CloudStack to get RBD support working:

1. RBD storage pool support in libvirt. [0] [1]
2. Fix a couple of bugs in the libvirt-java bindings. [2]

With those issues addressed I could implement RBD inside CloudStack.

While doing so I ran into multiple issues inside CloudStack which 
delayed everything a bit.

Now, the RBD support for primary storage knows limitations:

- It only works with KVM

- You are NOT able to snapshot RBD volumes. This is due to CloudStack 
wanting to backup snapshots to the secondary storage and uses 'qemu-img 
convert' for this. That doesn't work with RBD, but it's also very 
inefficient.

RBD supports native snapshots inside the Ceph cluster. RBD disks also 
have the potential to reach very large sizes. Disks of 1TB won't be the 
exception. It would stress your network heavily. I'm thinking about 
implementing "internal snapshots", but that is step #2. For now no 
snapshots.

- You are able create a template from a RBD volume, but creating a new 
instance with RBD storage from a template is still a hit-and-miss. 
Working on that one.

Other than these limitations, everything works. You can create instances 
and attach RBD disks. It also supports cephx authorization, so no 
problem there!

What do you need to run this patch?
- A Ceph cluster
- libvirt with RBD storage pool support (>0.9.12)
- Modified libvirt-java bindings (jar is in the patch)
- Qemu with RBD support (>0.14)
- A extra field "user_info" in the storage pool table, see the SQL 
change in the patch

You can fetch the code on my Github account [3].

Warning: I'll be rebasing against the master branch regularly, so be 
aware of git pull not always working nicely.

I'd like to see this code reviewed while I'm working on the latest stuff 
and getting all the patches upstream in other projects (mainly the 
libvirt Java bindings).

Any suggestions or comments?

Thank you!

Wido


[0]: 
http://libvirt.org/git/?p=libvirt.git;a=commit;h=74951eadef85e2d100c7dc7bd9ae1093fbda722f
[1]: 
http://libvirt.org/git/?p=libvirt.git;a=commit;h=122fa379de44a2fd0a6d5fbcb634535d647ada17
[2]: https://github.com/wido/libvirt-java/commits/cloudstack
[3]: https://github.com/wido/CloudStack/commits/rbd

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