[Engine-devel] SharedRawDisk feature detail

[Itamar Heim]

On 02/02/2012 05:15 PM, Maor wrote:
> Hello all,
>
> The shared raw disk feature description can be found under the following
> links:
>    http://www.ovirt.org/wiki/Features/DetailedSharedRawDisk
>    http://www.ovirt.org/wiki/Features/SharedRawDisk
>
> Please feel free, to share your comments.

1. Affected oVirt projects
i'm pretty sure the history data warehouse will need to adapt to this.

2. "The shared raw disk feature should provide the ability to attach 
disk to many VMs with safe concurrent access,"
this could be read as if ovirt or vdsm somehow provides a mechanism for 
safe concurrent access.
maybe something like "to multiple VMs that can handle concurrent access 
to a shared disk without risk of corruption".
and having just written this - sounds like setting this flag at UI level 
should include a prompt to the user to make sure they understand that 
flagging the disk as shared *will* lead to corruption if it is attached 
to virtual machines which do not support and expect it to be shared with 
other virtual or physical machines[1]

3. "The synchronization/clustering of shared raw disk between VMs will 
be managed in the file system. "

either i don't understand what this mean, or it could be read with a 
misleading meaning.

4. VM Pools
VM Pools are always based (at least today) on templates, and templates 
have no shared disks.
I'd just block attaching a shared disk to a VM which is part of a pool 
(unless there is a very interesting use case meriting this)

5. "Quota has to be taken in consideration, for every new feature that 
will involve consumption of resources managed by it."

I thought quota is not relevant in this feature.

6. future work - Permissions should be added for disk entity
so who can add a shared disk?
same as for floating disks, i find it hard to imagine a flow in which if 
someone flagged a disk as shared, suddenly everyone can have access to it.
same as my statement of floating disks - I'll spend some more time to 
reflect on this specific part.

[1] an external LUN based disk could be shared with a physical server as 
well.