nova-feature-parity team mailing list archive

[Vishvananda Ishaya <vishvananda@xxxxxxxxx>]

FYI on the kvm side, we use the --use_cow_images flag to toggle on this behavior, so someone who sets --nouse_cow_images will get a raw image.  That said, we don't redownload the image from glance every time.  We keep a local cache of the base image and do a straight file copy instead of a cow snapshot if the flag is false. It would be great to use the same flag for xen.

Potential future changes:
a) provide two flags, one for root drive, and one for local ephemeral storage
b) allow this to be set per instance instead of globally (perhaps keyed off of instance type)
c) expose it to the user? (allow them to specify whether they want cow images or not)


Vish

On Nov 8, 2011, at 8:53 PM, Paul Voccio wrote:

> Ewan,
> 
> I do think this is a needed feature and I would welcome any code that would eliminate bottlenecks within the system. 
> 
> Would this be optional or a fundamental change to how the images work? There are some assumptions within the code that a vm owns the entire vdi tree. I have a feeling the code could get messy if it is optional, but would create some bugs the short term while we sort this all out. However the approach, I do feel this is the right way to go. 
> 
> I spoke to some people who had the concern that there may be hotspots on the disk if we get too many vdis pointing to the same parent vdi. I don't yet share concern for this issue, but it is something to be aware of. 
> 
> I look forward to seeing what has been done so far. 
> 
> pvo
> 
> From: Ewan Mellor <Ewan.Mellor@xxxxxxxxxxxxx>
> Date: Wed, 9 Nov 2011 04:24:23 +0000
> To: "nova-feature-parity@xxxxxxxxxxxxxxxxxxx" <nova-feature-parity@xxxxxxxxxxxxxxxxxxx>, Paul Voccio <paul.voccio@xxxxxxxxxxxxx>, Vishvananda Ishaya <vishvananda@xxxxxxxxx>
> Cc: Devdeep Singh <devdeep.singh@xxxxxxxxxx>, Likitha Shetty <likitha.shetty@xxxxxxxxxx>
> Subject: Thin-cloning of disks for XenServer
> 
>> Hi,
>>  
>> I’d like to introduce Devdeep Singh and Likitha Shetty (both cc’d) from the Citrix OpenStack team in Bengaluru.  They are starting work on a feature for XenServer where the VM disk is streamed fromGlance the first time, and then future requests for that image are thin-cloned from the original, rather than streaming the image a second time from Glance.  This is something that is already implemented for KVM, so I presume that there is interest from the nova-feature-parity team.
>>  
>> As far as I can see there is no blueprint for this yet, so Devdeep and Likitha will start by publishing what they’ve got so far.  Your feedback is welcome.
>>  
>> Pvo, in particular I remember at the last summit that you had strong views on how this should work.  Any insight you have would be appreciated.
>>  
>> If there are any problems with the timezone difference to India then please let me know – I’ll address any communication issues.
>>  
>> Thanks,
>>  
>> Ewan.
>>