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On 02/10/2015 06:14 AM, Valeriy Ponomaryov wrote:
> Hello Jason,
>
> On Tue, Feb 10, 2015 at 10:07 AM, Jason Bishop <jason.bishop at gmail.com 
> <mailto:jason.bishop at gmail.com>> wrote:
>
>     When a share is created (from scratch), the manila scheduler
>     identifies a share server from its list of backends and makes an
>     api call to create_share method in the appropriate driver.  The
>     driver executes the required steps and returns the export_location
>     which is then written to the database.
>
> It is not correct description of current approach. Scheduler handles 
> only capabilities and extra specs, and there is no logic for filtering 
> based on share servers for the moment.
> Correct would be following:
> Scheduler (manila-scheduler) chooses host, then sends request "create 
> share" to chosen manila-share service, which handles all stuff related 
> to share servers based on share driver logic.

This is something I'd like to change. The scheduler should know about 
where the existing (usable) share servers are, and should be able to 
prefer a backend with an existing share server over a backend with no 
existing share server for share types that would require share servers. 
The administrator should control how strongly to weigh this information 
within the scheduler.

> On Tue, Feb 10, 2015 at 10:07 AM, Jason Bishop <jason.bishop at gmail.com 
> <mailto:jason.bishop at gmail.com>> wrote:
>
>     Proposed scheme:
>
>     The proposal is simple in concept.  Instead of the driver
>     (GenericShareDriver for example) returning both share server ip
>     address and path in share export_location, only the path is
>     returned and saved in the database.  The binding of the share
>     server ip address is only determined at share mount time.  In
>     practical terms this means share server is determined by an api
>     call to the driver when _get_shares is called.  The driver would
>     then have the option of determining which IP address from its
>     basket of addresses to return.  In this way, each share mount
>     event presents an opportunity for the NFS traffic to be balanced
>     over all available network endpoints.
>
> It is specific only to GenericShareDriver and mentioned public IP 
> address is used once for combining export_location from path and this 
> IP. Other share drivers do not store it and not forced to do it at 
> all. For example, in case of share driver for NetApp Clustered Data 
> OnTap stored only one specific information, it is name of vserver. IP 
> address is taken each time via API of backend.
>
> It is true, that now we have possibility to store only one export 
> location. I agree, that it would be suitable to have more than one 
> export_location. So, idea of having multiple export_locations is good.

We absolutely need multiple export locations. But I want that feature 
for other reasons than what Jason mentions. Typically, load balancing 
can be achieved by in-band techniques such as pNFS which only needs one 
export location to get started. The main value of the multiple export 
locations for me is to cover cases when a client wants to perform a 
mount during a failover event when one or more export locations are 
temporarily unreachable.


>
> On Tue, Feb 10, 2015 at 10:07 AM, Jason Bishop <jason.bishop at gmail.com 
> <mailto:jason.bishop at gmail.com>> wrote:
>
>     I see following cons:
>
>        o slow manila list performance
>
>        o very slow manila list performance if all share drivers are
>     busy doing long operations such as create/delete share
>
> First of all, manila-api service does know nothing about share drivers 
> or backends, that are meanings of different service/process - 
> manila-share, manila-api uses DB for getting information.
> So, you just can not ask share drivers with "list" API call. API 
> either reads DB and returns something or sends some RPC and returns 
> some data and does not expect result of RPC.
> If you want to change IP addresses, then you need to update DB with 
> it. Hence, it looks like requirement to have "periodic" task, that 
> will do it continuously.

Yes. Changing IP addresses would be a big problem because right now 
manila doesn't provide a way for the driver to alter the export location 
after the share is created.

> I prefer to have more than one export locations and allow users to 
> chose any of them. Also I assume possibility when IP addresses just 
> changed, in this case we should allow to update export locations.
>
> And second, if we implement multiple export locations for shares, 
> better to not return it within "list" API response and do it only 
> within "get" requests.

Agreed.

> Valeriy
>
>
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