Constraints

Performance requirements

The CTA metadata performance requirements have been assessed in previous work (see cta.pdf: Object Store/Performance considerations). Efficient metadata handling is particularly important for repacking, where small files can be encountered.

The data-taking performance might be less stringent in terms of metadata, but involves a bigger stack with EOS in front. This should be assessed in order to have full system performance targets. This includes the bandwidth to be achieved and the latency experienced by the user (a synchronous close on write will increase latency, we should make sure the result is adequate).

Synchronous calls

The EOS workflow engine will support synchronous actions. EOS clients will call EOS which in turn will call CTA. CTA will send back a "return value" reply which will be synchronously relayed back to the EOS client.

Example: An EOS client opens a file for creation that should be eventually archived to tape. EOS synchronously calls CTA to determine whether or not the Storage Class of the file is known and that it has a destination tape pool. If these two conditions are not met then the EOS client will get an immediate synchronous reply saying the file cannot be created because it cannot be archived to tape.