Spec Lite: Add new share server limits

problem

An administrator is not able to specify how many shares can be created in a given share server, nor the maximum size that a share server can hit. The current behavior allows the system to allocate a bunch of shares in a single share server and it allows the share server to reach a huge size, making it a bit harder to manage.

solution

We should add a limit for the amount of shares that a share server can hold. Administrators can configure this limit for each backend, and have more control over the size of share servers, which helps them to manage the cloud resources. The proposed solution introduces two new backend properties called max_shares_per_share_server and max_share_server_size, whereby the administrators are able to determine the amount of shares that can be created upon a given share server. Configuring the max_shares_per_share_server property means that a share server which reached the limit of shares will be filtered out of the compatible share servers list in the share manager. For the max_share_server_size backend capability, when a given share server hits the specified amount of gigabytes, the share manager will filter the share server out of the compatible share server list, and a new share server is going to be provided. In this case, not only shares are going to be considered in the final gigabytes amount, but share replicas and snapshots will be considered as well. If one of these backend capabilities is not set in the chosen backend, the share manager will understand that there is no limit for shares or gigabytes in that backend share servers. The share manager provide_share_server_for_share and provide_share_server_for_share_group methods will be modified to also check if there is a configured limit in the corresponding backend session in the Manila configuration file. These new limits can be implemented as mutable, which means an administrator won’t need to restart any service to have the changes applied. If at least one of the properties was specified, the share manager will query the amount of existent share server resources using the database layer for performance purposes, and finally, if needed, request the creation of a new share server to place the received request. When the limits are reached, no exceptions are being raised and the users or admins won’t be impacted by this. The share manager itself will handle with the situation by providing a new share server.

impacts

This implementation slightly impacts performance only when at least one of the backend capabilities was set, but there is no expectation to increase significantly the share creation time, specially compared to another possible approach where we ask the drivers to calculate the amount of resources in a given share server. Administrators must be aware that when configuring one of these limits more network allocations may be needed.

alternative

As an alternative we could use share type extra specs to provide driver specific limits for share server shares and max share server size in gigabytes. This approach would work in a project level, but we should consider that it may require the share manager to forward more information to the driver than we do today, in order to avoid driver calls to the storage which would cause a performance deterioration.

timeline

Include in Victoria release.

link

https://etherpad.opendev.org/p/victoria-ptg-manila https://review.opendev.org/#/c/510542/ https://blueprints.launchpad.net/manila/+spec/new-share-server-limits

assignee

carloss