Open Stack

Le 14/05/2013 18:37, Eric Harney a écrit :
> On 05/14/2013 11:03 AM, Joe Topjian wrote:
>> Hello,
>>
>> I thought I would post this due to the frequent Gluster talk on the 
>> list:
>>
>> Just an FYI for anyone thinking of using this volume driver: make 
>> sure you
>> are using a kernel greater than 3.3. For Ubuntu 12.04, the 3.4 kernel 
>> found
>> here works:
>> http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.4-precise/
>>
>> The reason for this is that Nova tries to attach the volume using
>> cache="none". This requires the filesystem to support O_DIRECT, which is
>> only available for FUSE-based filesystems in kernels above 3.3.

>> [...]

>> Finally, this issue seems to be resolved for using Gluster as an 
>> instance
>> store. If I remember right, I ran into this same issue several months 
>> ago
>> and it was resolved by updating the kernel. Seems like Grizzly correctly
>> detects if O_DIRECT is available or not.
>>
>> Thanks,
>> Joe
>>
>>
>
>
> Fixing this properly in Nova is on my to-do list.  It is correct that 
> it works for the Nova instance store, the problem is just for Cinder 
> volumes.
>
>


Indeed : the issue is only appearing when booting from volume. AFAIK, 
there was some trouble Essex ago with the FUSE filesystems and the 
libvirt disk caching parameter as cache=none.
The team provided a bugfix [1] assuming that if FUSE-based, then 
cache=writethrough, which could explain why Nova instance store is not 
impacted. I also know that the libvirt.xml generation has totally been 
rewritten in Folsom, you may have to check how they did.

Let me know once you post in Gerrit, I'll review it.
Btw, if [2] is done, then we should review if the issue will still be 
present, as it will use a new filesystem driver.

-Sylvain

[1] : https://bugs.launchpad.net/nova/+bug/959637
[2] : https://blueprints.launchpad.net/nova/+spec/glusterfs-native-support