On 02/10/2015 06:14 AM, Valeriy Ponomaryov wrote:
Hello Jason,

On Tue, Feb 10, 2015 at 10:07 AM, Jason Bishop <jason.bis...@gmail.com <mailto:jason.bis...@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.bis...@gmail.com <mailto:jason.bis...@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.bis...@gmail.com <mailto:jason.bis...@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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