[Engine-devel] Quota feature description

[Maor]

Hi Saggi, thanks for the comments, please see my comments in line

On 11/17/2011 02:36 PM, Saggi Mizrahi wrote:
> On Wed 16 Nov 2011 02:48:40 PM IST, Maor wrote:
>> Hello all,
>>
>> The Quota feature description is published under the following links:
>>    http://www.ovirt.org/wiki/Features/DetailedQuota
>>    http://www.ovirt.org/wiki/Features/Quota
>> Notice that screens of UI mockups should be updated.
>>
>> Please feel free, to share your comments about it.
>>
>> Thank you,
>> Maor
>>
>> _______________________________________________
>> Engine-devel mailing list
>> Engine-devel at ovirt.org
>> http://lists.ovirt.org/mailman/listinfo/engine-devel
> 
> I can't see how the host is supposed to enforce and handle it. Pause the
> VM? Crash it? raise ENOMEM\ENOSPC in the guest?
The enforcement and handling, should be from the engine scope and not
from the Host perspective.
Actually the Host, should not be aware of Quota at all.
> Also what about cases of KSM\QCow2, disk\memory overcommit.
on QCOW issue, the active disk should consume the full potential space
from the Quota, since we are not sure how much space will be in use,
slthough the snapshot disk, will be updated to consume only its real
size from the Quota.

you can check the Enforcement section :
"When dealing with QCOW disks (which is not pre-allocated, like
templates or stateless VM) the Quota should consume the total maximum
size of the disk, since it is the potential size that can be used."

for overcommit issue, please see CRUD section in the WIKI:
"...However, users will not be able to exceed the Quota limitations
again after the resources are released."

> Disk Templates.
> Storage for hibernation disk.
> Temporary and shared disks.
same logic as above (Enforcement section)
> Shared disks between VMs owned by different users.
Please see Dependencies / Related Features and Projects:
"When handling plug/unplug disks or attach/detach disks, the entity will
still consume resources from its configured original Quota it was
created on. "

Which means the disk should consume from the same Quota all the time
(not dependent on the users that use it).
> Backup snapshots (should they count in the quota? They are transient)
When ever a volume is created whether it is snapshot, backup snapshot,
stateless disk, or any QCOW implementation, the enforcement should the
the same as described above (see Enforcement section)
> 
> I also don't see how vcpu limiting is any good? I don't even know what
> it means. What happens in migration between hosts with different amount
> of physical CPUs?
The "atomic" section that Quota is handling in the run time scope is
cluster.
Actually for the user migration will be transparent since it is consumed
from the same Quota, the only validation the VM should encounter will be
the same as before in the Host perspective.

> I also don't think CPU limiting is even a thing to be managed by a
> quota. There is no reason not to use 100% of the CPU if you are the only
> VM active. CPU scheduling should use a priority model and not a quota IMHO.
Again, the Quota should be managed from the engine level, and should not
be reflected in the Host implementation.
Try to look at it, as an abstract management mechanism for taking notes
and managing resource consumes for the Administrator.

A priority model is an interesting thought.
Now it can be supported, by using different grace percentage from one
Quota to another, or maybe create different Quota for Different type of
users.