[Engine-devel] SPM Priority Design - Wiki Page

[Yaniv Kaul]

On 12/29/2011 04:34 PM, Andrew Cathrow wrote:
>
> ----- Original Message -----
>> From: "Itamar Heim"<iheim at redhat.com>
>> To: "Miki Kenneth"<mkenneth at redhat.com>
>> Cc: engine-devel at ovirt.org
>> Sent: Thursday, December 29, 2011 5:41:41 AM
>> Subject: Re: [Engine-devel] SPM Priority Design - Wiki Page
>>
>> On 12/27/2011 05:22 PM, Miki Kenneth wrote:
>>> Few points:
>>> - From requirement perspective - 0-10 scale is OK too.
>>> - There is an RFE to allow manual SPM selection, let's make sure
>>> that we clarify how we do that in the scenarios.
>>> - There is a case were all Hosts are set as "no SPM" (-1), user
>>> should be notify (on the last host?)
> I don't agree with/understand the requirements
> <snip>
> - Enable setting a priority between -1 and 100 for a host (100 is the highest, -1 means never to choose this host).
> - When SPM selection process takes place, use the SPM priority to select an SPM.
> - Default for upgrading ovirt will be 50.
> </snip>
>
> Here we are asking the user to define priorities for the SPM selection. A user should be able to influence the selection but the actual choice should come down to runtime status.
> If Host A us running 100 VMs and host B is running 50 then it seems more efficient for B to be the SPM rather than A
> If Host C has multiple storage paths to the LUN then it seems a better fit than host B that has only one path.
>
> We need to step back and review the requirements here.
>
> Today SPM selection is random, that certainly needs to change but a user defining priorities is overly complex and won't solve the runtime selection issue.
>
> We need to start by defining an algorithm for selecting the SPM independent of user input.
> At selection time I'd suggest that we at least need to consider number of paths to the storage (for block based) number of VMs on that host, perhaps #cores?

Paths to which storage domain? the master? all? on average?
Do you prefer 2x10Gb iSCSI connection, or 4x1Gb?

- What about available bandwidth to the storage (assuming it may be 
capped and compete with VM IO traffic) ?
- Latency?

> Perhaps we should dynamically create a score for a host that takes these factors into account, each may get higher rating - eg. maybe # storage paths is more important that # cores ?

This is why I've suggested High(8)-Med(5)-Low(2) and add dynamically the 
system scoring, with whatever params we get to eventually. 'Never' could 
be 0, 'Always' could be '10'.
Y.

>
>
> On top of this we can add some user defined preference that plays into the score. For example a user can say "this host can NEVER be an SPM" or can set a preference - eg. "Preferred SPM" or perhaps even "always SPM"
>
> This algorithm would apply for automated selection of SPMs but a user should be allowed to override this and at runtime say "make this node the SPM now"
>
>
>
>> SPM is DC level, not cluster level.
>>
>>> - Need to be able to view in the GUI:
>>>     - the SPM priority for all Hosts, on the GRID?
>> isn't this cluttering the hosts grid? general subtab maybe?
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