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From Chiradeep Vittal <Chiradeep.Vit...@citrix.com>
Subject Re: First review of RBD support for primary storage
Date Thu, 05 Jul 2012 22:54:27 GMT
I took a first glance at this. Really pleased about this feature. EBS-like
scalable primary storage is within reach!

A few comments:
 1. I see quite a few blocks of code ( > 20 times?) that are like
     if (pool.getType() == StoragePoolType.RBD)
    I realize that there is existing code that does these kinds of checks
as well. To me this can be solved simply by the "chain of responsibility"
pattern: you hand over the operation to a configured chain of handlers.
The first handler (usually) that says it can handle it, terminates the
chain. 
 2. 'user_info' can actually be pushed into the 'storage_pool_details'
table. Generally we avoid modifying existing tables if we can.
 3. Copying a snapshot to secondary storage is desirable: to be consistent
with other storage types, to be able to instantiate new volumes in other
zones (when S3 support is available across the region). I'd like to
understand the blockers here.


On 7/2/12 5:59 AM, "Wido den Hollander" <wido@widodh.nl> wrote:

>Hi,
>
>On 29-06-12 17:59, Wido den Hollander wrote:
>> 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.
>>
>
>I just pushed a fix for creating instances from a template. That should
>work now!
>
>Wido


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